A debt of $20,000 is repaid by making payments of $3500. If interest is 9% compounded monthly, for how long will payments have to be made? (a) at the end of every six months? (b) at the beginning of each year? (c) at the end of every three months with payments deferred for five years? (d) at the beginning of every six months with payments deferred for three years? (a) Payments have to be made for semi-annual periods. (Round up to the nearest whole number.)