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11. [8] Marry borrows $15000 for 10 years. She makes total payments, annually, of $2000. The lender receives ji = 10% on his investment each year for the first 5 years and ji = 8% for the second 5 years. The remaining of each payment is invested in a sinking fund earning 11 = 7%. (a) Determine the amount by which the sinking fund is short of repaying the loan at the end of 10 years; (b) By how much would the sinking-fund deposit (in each of the first 5 years only) need to be increased so that the sinking fund at the end of 10 years will be just sufficient to repay the loan