IRREVOCABLE LETTER OF CREDIT





Letter of Credit No. G/LA-400557                                 August 5, 1997



First Trust of California, National Association
not individually but solely as Trustee
One California Street, Fourth Floor
San Francisco, California 94111

Attention:  Corporate Trust Department

Ladies and Gentlemen:

         We hereby issue in your favor, not individually,  but solely as Trustee
(the  "Trustee")  under the  Indenture  of Trust dated as of August 1, 1997 (the
"Indenture")  between the California  Economic  Development  Financing Authority
(the  "Issuer")  and you,  this  irrevocable  direct pay letter of credit  (this
"Letter of Credit") in an amount not exceeding $8,625,754 (the "Stated Amount"),
of which an amount not  exceeding  $8,500,000  may be drawn upon with respect to
the  payment of  principal  of the  Issuer's  $8,500,000  Variable  Rate  Demand
Industrial  Development  Revenue Bonds,  Series 1997 (Advanced  Aerodynamics and
Structures, Inc. Project) (the "Bonds") and an amount not exceeding $125,754 may
be drawn upon with respect to the payment of up to forty-five (45) days' accrued
interest  (at the rate of 12% per annum  based on a 365-day  year) on the Bonds,
for payment of your draft, drawn at sight on The Sumitomo Bank, Limited,  acting
through its Los Angeles Branch (the "Bank"),  777 South Figueroa  Street,  Suite
2600, Los Angeles,  California 90017 (or such other address in the United States
of America as may be designated to you in writing from time to time by the Bank)
accompanied   by  your   signed   certificate   (with  the   blanks   filled  in
appropriately):

         1. if the  drawing  is  being  made  with  respect  to the  payment  or
provision for payment of interest on the Bonds,  whether for regularly scheduled
interest  payments  pursuant  to Section  2.02 of the  Indenture  or for accrued
interest  on Bonds  subject to  optional  or  mandatory  redemption  pursuant to
Article IV of the Indenture or upon the  acceleration  of the Bonds  pursuant to
Section 7.01 of the Indenture, your certificate in the form attached as Annex I;

         2. if the  drawing  is  being  made  with  respect  to the  payment  of
principal upon an optional or mandatory  redemption of Bonds pursuant to Article
IV of the  Indenture or upon the maturity of the Bonds  pursuant to Section 2.02
of the Indenture or upon the  acceleration of the Bonds pursuant to Section 7.01
of the Indenture, your certificate in the form attached as Annex II;


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         3. if the  drawing is made with  respect to the  payment of the accrued
interest and the principal  portion of the purchase  price of Bonds  tendered or
deemed to have been  tendered  pursuant to Section  4.06 or Section  4.07 of the
Indenture,  your  certificate  in the form attached as Annex III (any such draft
accompanied  by such  signed  certificate  is herein  referred to as a "Purchase
Price Draft").

         More than one demand  for  payment  may be made  under  this  Letter of
Credit.  A demand for  payment  with  respect to the  payment of  interest on or
principal  of the Bonds  shall not exceed  that  portion  of the  Stated  Amount
allocated  to interest  or  principal,  respectively,  as the same is reduced or
reinstated from time to time as provided below.

         The expiration  date of this Letter of Credit (the  "Expiration  Date")
shall be the  earliest  of:  (i) our  close of  business  on August 5, 2002 (the
"Stated Expiration  Date"),  unless the Stated Expiration Date has been extended
and the Stated Amount adjusted (if  appropriate) by an instrument  substantially
in the form of  Attachment C hereto (which forms an integral part of this Letter
of  Credit);  (ii) ten (10) days after you  receive  notice  from the Bank of an
Event of Default under (and as defined in) the Reimbursement Agreement dated as.
of August 1, 1997  between  Advanced  Aerodynamics  and  Structures,  Inc.  (the
"Company") and the Bank (the "Reimbursement Agreement") and a direction to cause
a redemption of all  outstanding  Bonds under the terms of the Indenture;  (iii)
the date on which the Bank,  receives  notice  from you that all Bonds have been
paid in full or such payment has been provided for in accordance  with the terms
of the  Indenture;  (iv)  the date on  which  the  Bonds  become  secured  by an
Alternate  Letter of Credit (as defined in the Indenture) in accordance with the
terms of the Indenture; and (v) the date on which the interest rate on the Bonds
is  converted  to a fixed rate of interest in  accordance  with the terms of the
Indenture.  You  shall  surrender  this  Letter  of  Credit  to the  Bank on the
Expiration Date of this Letter of Credit.

         A draft and completed signed  certificate  (other than a Purchase Price
Draft)  presented prior to 9:00 a.m., Los Angeles,  California  time, on any day
except Saturday, Sunday or any day on which banking institutions located, in the
Cities of New York, New York or Los Angeles, California or the city in which the
principal  office of the  Trustee or the  Remarketing  Agent (as  defined in the
Indenture) is located  (initially,  San Francisco,  California)  are required or
authorized  by law to close or a day on which  the New York  Stock  Exchange  is
closed (a  "Business  Day") shall be honored and the amount of the draft paid in
immediately  available funds by 1:00 p.m., Los Angeles,  California time) on the
same Business Day,  provided  that such draft and signed  certificate  presented
conform  to the terms and  conditions  of this  Letter  of  Credit.  A draft and
completed signed certificate (other than a Purchase Price Draft) presented after
9:00 a.m., Los Angeles, California time on any Business Day shall be honored and
the amount of the draft paid in  immediately  available  funds by 11:00 a.m. Los
Angeles,  California  time,  on the following  Business Day,  provided that such
draft and signed  certificate  presented  conform to the terms and conditions of
this Letter of Credit.  A Purchase Price Draft presented prior to 9:00 a.m., Los
Angeles, California time, on any Business Day shall be honored and the amount of
the  draft  paid in  immediately  available  funds  by 1:00  p.m.  Los  Angeles,
California  time on the same  Business Day,  provided  that such Purchase  Price
Draft presented conforms to the terms and conditions of this Letter of Credit. A
Purchase Price Draft presented after

                                        2





9:00 a.m., Los Angeles, California time on any Business Day shall be honored and
the amount of the draft paid in immediately  available  funds by 11:00 a.m., Los
Angeles, California time on the following Business Day, provided that such draft
and signed  certificate  presented  conform to the terms and  conditions of this
Letter  of  Credit.  Payment  under  this  Letter  of  Credit  shall  be made in
accordance with the payment instructions set forth in the completed  certificate
accompanying  each  draft.  All  payments  made by the Bank under this Letter of
Credit shall be made from the Bank's own funds without any requirement  that the
Trustee,  the holders of the Bonds or the Bank make any prior claims against the
Company  and not out of any  funds of the  Company,  the  Issuer  or any  entity
related to either of them.  By the time set forth above on the Business Day such
payment is due the Bank shall  enter such  payment  instructions  on the Federal
Reserve  wire or, in the event  such  payment  instructions  specify  an account
maintained with the Bank, credit such account with immediately available funds.

         Any draft or certificate  may be presented in person to the Bank or may
be sent to the Bank by telecopier or other  electronic  communication,  promptly
confirmed  by  telephone  at (213) 955- 0800,  Attention:  Manager -  Structured
Finance and Financial  Institutions Group, to telecopy number (213) 623-6832 (or
such other  telecopy or telephone  number as may be designated to you in writing
from time to time by the  Bank).  Any such  draft or  certificate  presented  by
telecopy or other electronic  communication  shall be mailed or delivered to the
Bank on the same day to our  office  specified  in the first  paragraph  of this
Letter of Credit.

         This Letter of Credit is successively  transferable only to a successor
paying agent upon receipt by the Bank of prior  written  notice of such transfer
in accordance  with Attachment A (which forms an integral part of this Letter of
Credit),  acknowledged by a purported officer of the Trustee and the transferee,
addressed to the Bank and certifying that the transferee is a successor  trustee
under the Indenture.

         Each  payment of a draft with  respect to the payment of interest on or
principal of the Bonds honored by the Bank shall. pro Tanto, reduce that portion
of the  Stated  Amount  available  under  this  Letter  of  Credit.  subject  to
reinstatement as provided below.  Following the honoring of a drawing  hereunder
to pay regularly scheduled principal of the Bonds or principal of the Bonds upon
an optional or  mandatory  redemption  of the Bonds,  that portion of the Stated
Amount  available  under  this  Letter of Credit to pay  interest  shall also be
reduced to an amount equal to  forty-five  (45) days'  accrued  interest (at the
rate of  interest  of 12% per annum  based on a 365-day  year) on the  principal
amount of the remaining  outstanding Bonds (other than Pledged Bonds (as defined
in the Reimbursement Agreement)).  In addition, the Stated Amount of this Letter
of Credit  shall also be reduced  by the  amount  stated in a written  notice of
reduction  executed by a purported  officer of the Trustee  substantially in the
form of Attachment B (which forms an integral part of this Letter of Credit).  A
reduction  of the  Stated  Amount  through  the use of such a written  notice of
reduction  shall be  effective  as of the actual  date of receipt by the Bank of
such notice at its above-stated address.


                                        3





         The Stated Amount shall be reinstated as follows:

         (a) Following the honoring of a drawing under this Letter of Credit for
the  payment of the  purchase  price of Bonds  tendered,  or deemed to have been
tendered,  to the  Trustee or the  Tender  Agent (as  defined in the  Indenture)
pursuant to Section 4.06 or Section  4.07 of the  Indenture,  the Stated  Amount
shall be reinstated  automatically  and immediately  upon and to the extent that
you have received payment in immediately available funds of the principal of and
accrued interest on the Pledged Bonds in connection with the remarketing thereof
and are holding such  payment for the Bank's sole  benefit and account;  in such
case, (i) the principal  portion of this Letter of Credit shall be reinstated in
an amount equal to the  principal  amount of the  remarketed  Bonds and (ii) the
interest portion shall be reinstated to an amount equal to forty-five (45) days'
accrued interest on the Bonds outstanding (other than Pledged Bonds), calculated
at the rate of 12% per annum based on a 365-day year.  In connection  therewith,
you shall wire  transfer  such  payment to the Bank  immediately  after  receipt
thereof and you shall send to the Bank your telecopy  (promptly followed by mail
delivery) notifying the Bank of such payment.

         (b) Immediately following the honoring of a drawing hereunder to make a
regularly  scheduled interest payment on the Bonds (that is, other than interest
in connection with an optional  redemption or mandatory  redemption of the Bonds
in whole or in part or an  acceleration  or optional or mandatory  tender of the
Bonds)  in an  amount  set  forth  in the  certificate  in the  form of  Annex I
submitted in conjunction with such drawing, the Bank's obligation hereunder with
respect to the payment of interest on the Bonds will be automatically reinstated
by the amount of such drawing.

         (c) The  principal  and  interest  portions of the Stated  Amount shall
otherwise be reinstated as the Bank may from time to time notify you in writing.

         The Sumitomo Bank, Limited acknowledges and agrees, notwithstanding any
terms or provisions of this Letter of Credit or the  Reimbursement  Agreement to
the contrary, that this Letter of Credit is in all respects an obligation of The
Sumitomo Bank, Limited,  binding and enforceable against its properties,  assets
and revenues wherever located.

         This  Letter of Credit  shall be  governed  by the laws of the State of
California  including without  limitation,  Article 5 of the Uniform  Commercial
Code as in effect in the State of California,  as supplemented by the provisions
(to the extent such provisions are consistent with this Letter of Credit) of the
Uniform   Customs  and  Practice  for   Documentary   Credits  (1993   Revision)
International Chamber of Commerce, Publication No. 500 (the "Uniform Customs").


                                        4





         We undertake that your draft and certificate  drawn and presented on or
before the time of expiration  of this Letter of Credit in  conformity  with the
terms of this Letter of Credit will be duly honored.


                                       Very truly yours,

                                       THE SUMITOMO BANK, LIMITED


                                       By:____________________________________
                                        __________________, Los Angeles Branch




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ANNEX I (INTEREST DRAW) to 
Transferable  Irrevocable Direct Pay Letter of Credit
Issued by The Sumitomo Bank, Limited, acting through its Los Angeles Branch

The Sumitomo Bank, Limited (Los Angeles Branch)
777 South Figueroa Street, Suite 2600
Los Angeles, California 90017

Attention:        Manager - Structured Finance and
                  Financial Institutions Group

Gentlemen:

         We refer to  Transferable  Irrevocable  Direct Pay Letter of Credit No.
G/LA-400557 issued in support of the $8,500,000  California Economic Development
Financing  Authority Variable Rate Demand Industrial  Development Revenue Bonds,
Series 1997 (Advanced Aerodynamics and Structures, Inc. Project) (the "Letter of
Credit"). Terms defined in the Letter of Credit and not otherwise defined herein
shall have the same meanings herein as therein.

         1. As the Trustee pursuant to the Indenture, in trust for the owners of
the Bonds,  we hereby make demand for payment  under the Letter of Credit to pay
or provide for the payment of unpaid  interest on such Bonds in connection  with
either a  regularly  scheduled  interest  payment,  an  optional  redemption,  a
mandatory  redemption or  acceleration  of the Bonds.  Such Bonds have been duly
authenticated under and in accordance with the Indenture.

         2.  Interest  on the  Bonds  is now or  will  under  the  terms  of the
Indenture become due and payable on or prior to the regularly scheduled interest
payment date,  maturity  date or redemption  date of the Bonds and the aggregate
amount  required  to  pay  or to  provide  for  the  payment  of  the.  same  is
$________________ and payment of such amount is hereby demanded.

         3. The amount demanded does not exceed the amount available today to be
drawn  under the Letter of Credit in respect of the  payment of  interest on the
Bonds.

         4. Upon receipt of the amount demanded under this Letter of Credit,  we
will  apply the same  directly  to the  payment  when due of  interest  owing on
account of the Bonds.


                                        6





         5. (Please wire the amount demanded hereunder to account no. __________
at  _______________  in __________  [Please credit account no. _____  maintained
with you.]

Dated as of __________ 19__.

                                        First  Trust  of  California,   National
                                        Association,  not in its  individual  or
                                        corporate   capacity,   but   solely  as
                                        Trustee under the Indenture.


                                        By:_____________________________________
                                        Title:__________________________________



                                        7





ANNEX II  (PRINCIPAL  DRAW) to  
Transferable  Irrevocable  Direct  Pay Letter of Credit  Issued by The  Sumitomo
Bank, Limited, acting through its Los Angeles Branch

The Sumitomo Bank, Limited (Los Angeles Branch)
777 South Figueroa Street, Suite 2600
Los Angeles, California 90017

Attention:        Manager - Structured Finance and
                  Financial Institutions Group

Gentlemen:

         We refer to  Transferable  Irrevocable  Direct Pay Letter of Credit No.
G/LA-400557 issued in support of the $8,500,000  California Economic Development
Financing  Authority Variable Rate Demand Industrial  Development Revenue Bonds,
Series 1997 (Advanced Aerodynamics and Structures, Inc. Project) (the "Letter of
Credit"). Terms defined in the Letter of Credit and not otherwise defined herein
shall have the same meanings herein as therein.

         1. As the Trustee pursuant to the Indenture, in trust for the owners of
the Bonds,  we hereby make demand for payment  under the Letter of Credit to pay
all or a portion of the unpaid  principal  amount of such Bonds  which have been
duly authenticated under and in accordance with the Indenture in connection with
either an  optional  redemption,  a  mandatory  redemption  or upon  maturity or
acceleration of the Bonds.

         2.  Principal  on the  Bonds  is now or will  under  the  terms  of the
Indenture  become due and payable on or prior to the maturity date or redemption
date of the Bonds;  the drawing in the amount of  $____________ is being made to
pay the principal portion of each such Bond and payment of such amount is hereby
demanded.

         3. The amount demanded does not exceed the amount available on the date
hereof to be drawn  under the  Letter of Credit in  respect  of the  payment  of
principal on the Bonds.

         4. Upon receipt of the amount demanded under this Letter of Credit,  we
will apply the same directly to the payment of the principal owing on account of
the Bonds.

         5. The  Stated  Amount of the  Letter of  Credit  shall be  permanently
reduced by the amount of the draw hereunder.


                                        8





         6. [Please wire the amount demanded hereunder to account no. __________
at _______________  in __________  [Please credit account no._______  maintained
with you.]

Dated as of __________, 19__.

                                        First  Trust  of  California,   National
                                        Association,  not in its  individual  or
                                        corporate   capacity,   but   solely  as
                                        Trustee under the Indenture.


                                        By:
                                        Title:



                                        9





ANNEX III (PURCHASE PRICE DRAW) to

Transferable  Irrevocable  Direct  Pay Letter of Credit  Issued by The  Sumitomo
Bank, Limited, acting through its Los Angeles Branch

The Sumitomo Bank, Limited (Los Angeles Branch)
777 South Figueroa Street, Suite 2600
Los Angeles, California 90017

Attention:        Manager - Structured Finance and
                  Financial Institutions Group

Gentlemen:

         We refer to  Transferable  Irrevocable  Direct Pay Letter of Credit No.
G/LA-400557 issued in support of the $8,500,000  California Economic Development
Financing  Authority Variable Rate Demand Industrial  Development Revenue Bonds,
Series 1997 (Advanced Aerodynamics and Structures, Inc. Project) (the "Letter of
Credit"). Terms defined in the Letter of Credit and not otherwise defined herein
shall have the same meanings herein as therein.

         1. As the Trustee pursuant to the Indenture,  we hereby make demand for
payment under the Letter of Credit to pay a part or all of the interest  portion
and the principal  portion of the purchase  price to be paid in respect of Bonds
which have been duly  authenticated  under and in accordance  with the Indenture
and which have been  tendered or were deemed to have been  tendered  pursuant to
Section 4.06 or Section 4.07 of the Indenture and for which remarketing proceeds
have not been received.

         2. The drawing in the aggregate  amount of $  _______________  is being
made to pay the purchase  price of Bonds which have been tendered or were deemed
to have been tendered.  Such aggregate  amount equals the sum of the amounts set
forth in paragraphs 3 and 5 below.

         3. The portion of the drawing equal to $ _______________  is being made
to pay a part or all of the interest portion of the purchase price of such Bonds
which have been  tendered  or were  deemed to have been  tendered  and for which
remarketing  proceeds  have  not  been  received  corresponding  to the  accrued
interest thereon, and payment of such amount is hereby demanded.

         4. Upon  receipt of the amount set forth under  paragraph  3 above,  we
will apply the same  directly  to the  payment of a part or all of the  interest
portion of the amount to be paid in respect of the Bonds.

         5. The portion of the drawing equal to $ _______________  is being made
to pay the principal portion of the purchase price of such Bonds which have been
tendered or were deemed to have been tendered and for which remarketing proceeds
have not been received, and payment of such amount is hereby demanded.

                                       10





         6. Upon  receipt of the amount set forth under  paragraph  5 above,  we
will apply the same  directly  to the  payment of the  principal  portion of the
purchase price to be paid in respect of the Bonds.

         7. The amount  set forth  under  paragraph  3 above does not exceed the
amount  available  on the date  hereof to be drawn under the Letter of Credit in
respect of the  payment of  interest on the Bonds and the amount set forth under
paragraph 5 above does not exceed the amount  available on the date hereof to be
drawn under the Letter of Credit in respect of the payment of  principal  on the
Bonds.

         8. [Please wire the amount demanded hereunder to account no. __________
at  _______________  in  __________.]  [Please  credit  account  no.  __________
maintained with you.]

Dated as of _______________ 19__.


                                        First  Trust  of  California,   National
                                        Association,  not in its  individual  or
                                        corporate   capacity,   but   solely  as
                                        Trustee under the Indenture.


                                         By:
                                         Title:



                                       11





                    ATTACHMENT A TO TRANSFERABLE IRREVOCABLE
                           DIRECT PAY LETTER OF CREDIT
                             (Transfer Certificate)

                                                     ____________________ 19__

The Sumitomo Bank, Limited (Los Angeles Branch)
777 South Figueroa Street, Suite 2600
Los Angeles, California 90017

Attention:        Manager - Structured Finance and
                  Financial Institutions Group

Gentlemen:

         We refer to Transfer-able  Irrevocable  Direct Pay Letter of Credit No.
G/LA-400557 issued in support of the $8,500,000  California Economic Development
Financing  Authority Variable Rate Demand Industrial  Development Revenue Bonds,
Series 1997 (Advanced Aerodynamics and Structures, Inc. Project) (the "Letter of
Credit").

         The undersigned is the Trustee  referred to in the Letter of Credit and
we  hereby  give you  notice  that  __________  is the  successor  Trustee  (the
"Successor  Trustee")  under the Indenture  referred to in the Letter of Credit,
and that the Successor  Trustee shall succeed to all the rights and  obligations
of the Trustee under the Letter of Credit.

         Upon payment to you of a $2,000  transfer fee by Advanced  Aerodynamics
and Structures,  Inc., your consent to the transfer of the Letter of Credit with
the date thereof to be confirmed by a

                                       12





Notary Public in Japan (or  otherwise  officially  established)  pursuant to the
laws of Japan and receipt by us of your acknowledgment and acknowledgment by the
Successor  Trustee of this notice,  the Letter of Credit shall be deemed to have
been transferred to the Successor Trustee.

                                        Very truly yours,

                                        First Trust of California, National 
                                        Association

                                        By:
                                        Title:

Agreed and Accepted:                    Acknowledged:

The Sumitomo Bank, Limited,             [Name of Successor Trustee]
acting through Its
Los Angeles Branch

By:_________________________________     By:
Title:______________________________     Title:
Date:_______________________________     Date:



                                       13





                    ATTACHMENT B TO TRANSFERABLE IRREVOCABLE
                           DIRECT PAY LETTER OF CREDIT
                             (Reduction Certificate)


                                                      ____________________ 19__

The Sumitomo Bank, Limited (Los Angeles Branch)
777 South Figueroa Street, Suite 2600
Los Angeles, California 90017

Attention:        Manager - Structured Finance and
                  Financial Institutions Group

Gentlemen:

         We refer to  Transferable  Irrevocable  Direct Pay Letter of Credit No.
G/LA-400557 issued in support of the $8,500,000  California Economic Development
Financing  Authority Variable Rate Demand Industrial  Development Revenue Bonds,
Series  1997  (Advanced   Aerodynamics   and   Structures,   Inc.   Project)  by
_______________ Dollars ($ __________). This reduction in Stated Amount shall go
to reduce that portion of the Stated Amount allocated to (principal, interest)1/
relating to the Bonds and shall be effective as of the actual date of receipt of
this instrument by The Sumitomo Bank, Limited. Accordingly, the Stated Amount of
the  Letter  of  Credit  after  giving  effect  to  such   reduction   shall  be
____________________  Dollars ($  _______________).  It is acknowledged that the
amount of such  reduction  shall no longer be  available  for  payment of drafts
under the Letter of Credit.  All terms used in this instrument which are defined
in the Letter of Credit shall have the same meaning in this instrument as in the
Letter of Credit.

                                        First  Trust  of  California,   National
                                        Association,  not in its  individual  or
                                        corporate   capacity,   but   solely  as
                                        Trustee under the Indenture  referred to
                                        in the Letter of Credit.


                                         By:
                                         Title:


- --------
1/ Complete as appropriate.

                                       14




                    ATTACHMENT C TO TRANSFERABLE IRREVOCABLE
                           DIRECT PAY LETTER OF CREDIT
                              (Notice of Extension)


                                                      ____________________ 19__


The Sumitomo Bank, Limited (Los Angeles Branch)
777 South Figueroa Street, Suite 2600
Los Angeles, California 90017

Attention:        Manager - Structured Finance and
                  Financial Institutions Group

Gentlemen:

         We refer to  Transferable  Irrevocable  Direct Pay Letter of Credit No.
G/LA-400557 issued in support of the $8.500,000  California Economic Development
Financing  Authority Variable Rate Demand Industrial  Development Revenue Bonds,
Series  1997  (Advanced  Aerodynamics  and  Structures,  Inc.  Project),  in the
original Stated Amount of $8,625,754 (the "Letter of Credit").  We hereby notify
you that, in accordance  with the terms of the Letter of Credit and that certain
Reimbursement   Agreement  dated  as  of  August  1,  1997,   between   Advanced
Aerodynamics and Structures, Inc. and us, the Stated Expiration Date (as defined
in the  Letter  of  Credit)  of the  Letter  of  Credit  has  been  extended  to
_______________.

         The portions of the Stated Amount of the Letter of Credit  available to
pay  principal  and  interest  on  the  Bonds  are  $   _______________   and  $
_______________, respectively, and the Stated Amount is $ _______________.

         This letter  should be attached to the Letter of Credit and made a part
thereof.

                                         THE SUMITOMO BANK, LIMITED
                                         LOS ANGELES BRANCH


                                         By:
                                         Its:




                                       15