(Present value of an annuity) What is the present value of the followingannuities?

a. 2,800 a year for 8 years discounted back to the present at 9percent.

b. $80 a year for 5 years discounted back to the present at 8 percent.

c. $280 a year for 13 years discounted back to the present at 12 percent.

d. $500 a year for 4 years discounted back to the present at 5 percent.