How much money can be withdrawn at the end of 15 years if

a. $\$2$,000 is deposited at the end of each year and earns 5 percent/year compounded annually?

b. $\$3$,000 is deposited at the end of each year for 10 years and no deposits are made thereafter, where the fund earns 8 percent?

c. $\$2$,000 is deposited at the end of years 1 through 5, $\$4$,000 is deposited at the end of years 6 through 10, and

$\$6$,000 is deposited at the end of years 11 through 15, with all deposits earning 8 percent?