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                                                                      EXHIBIT 12
 
                  RATIO OF EARNINGS TO COMBINED FIXED CHARGES
                         AND PREFERRED STOCK DIVIDENDS
 
     The ratio of earnings to combined fixed charges and preferred stock
dividends are as follows:
 


                                                                        YEAR ENDED DECEMBER 31
                                                             --------------------------------------------
                                                             1997      1996      1995      1994      1993
                                                             ----      ----      ----      ----      ----
                                                                                      
Ratio of Earnings to Combined Fixed Charges and Preferred
  Stock Dividends(1).......................................  2.60X     2.66X     2.92X     2.69X     3.51X

 
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(1) For purposes of calculating the ratio of earnings to combined fixed charges
    and preferred stock dividends, net earnings (before extraordinary charge
    from prepayment of debt in 1995) has been added to fixed charges and that
    sum has been divided by such fixed charges. Fixed charges consist of
    interest expense, amortization of deferred financing costs and, starting
    with the period ended December 31, 1997, preferred stock dividends for the
    Series A Cumulative Preferred Stock, which is the only series of preferred
    stock outstanding at December 31, 1997.