(Present value of an annuity)

What is the present value of the following annuities?

a.$2,500 a year for 10 years discounted back to the present at 7 percent.

b. $70 a year for 3 years discounted back to the present at 3 percent.

c. $280 a year for 7 years discounted back to the present at 6 percent.

d. $50 a year for 10 years discounted back to the present at 10 percent.

(Round to the nearest cent.)