EXHIBIT 10.4





April 28, 2000


Thomas E. Dooley
Deputy Chairman
Viacom Inc.
1515 Broadway
New York, New York  10036



Dear Tom:

                  This letter is intended to confirm certain of our
understandings relating to the Agreement between you and Viacom Inc. (the
"Company"), dated as of September 6, 1999 (the "Agreement").

                  You have agreed to resign your employment as an employee of
the Company and any of the Company's direct or indirect subsidiaries and your
position as an officer of the Company as Deputy Chairman and Executive Vice
President. You further have agreed to resign as an officer and member of the
boards of directors of the Company's direct and indirect subsidiaries (except as
noted in the following sentence). It is our mutual intention that you shall
continue as a member of the boards of directors of the Company, Blockbuster Inc.
and The MTVi Group, Inc. for the remainder of your current term. All
resignations shall be effective as of the day immediately prior to the Effective
Time of the closing of the transactions contemplated by the Agreement and Plan
of Merger between CBS Corporation and the Company, dated as of September 6,
1999. The Company acknowledges that such resignation is at the request, and for
the benefit, of the Company, shall be deemed to constitute termination of your
employment for "Good Reason" (and for this purpose the Company waives any
written notice from you or any period within which to cure) and the Resignation
Date for purposes of the Agreement shall be deemed to include the date of such
resignation thereby qualifying you for all the payments and benefits attendant
to a resignation for Good Reason or a resignation on the Resignation Date, under
the Agreement, and the Restricted Period for purposes of Section 4.1 of the
Agreement shall commence on such Resignation Date.


                  Please acknowledge your assent to the foregoing by executing
the attached copy of this letter agreement where indicated and returning it to
the Company.

                                                     Very truly yours,

                                                     /s/ Michael D. Fricklas




ACCEPTED AND AGREED:



  /s/ Thomas E. Dooley
- --------------------------------
   Thomas E. Dooley