ordinary annuities

Find the future values of the following ordinary annuities:
a. FV of $400 each six months for five years at a simple rate of 12 percent, compounded semiannually
b. FV of $200 each three months for five years at a simple rate of 12 percent, compounded quarterly
c. The annuities described in parts a and b have the same amount of money paid into them during the five-year period and both earn interest at the same simple rate, yet the annuity in part b earns $101.75 more than the one in part a over the five years. Why does this occur?