15. An investment of $21 700 is accumulated at 5.24% compounded quarterly for three and one-half years. At that time the interest rate is changed to 6.12% compounded monthly. How much is the investment worth two years after the change in interest rate? 16. A loan of $4500.00 was repaid together with interest of $1 164.00. If interest was 12 .4% compounded quarterly, for how many months was the loan taken out? 17. Doris purchased a piano with $1300.00 down and monthly payments of $214.00 for two years at 9.72% compounded monthly. What was the purchase price of the piano