(Present value of an annuity) What is the present value of the following annuities? a. $2,800 a year for 9 years discounted back to the present at 11 percent. b. $60 a year for 4 years discounted back to the present at 7 percent. c. $300 a year for 11 years discounted back to the present at 12 percent. d. $430 a year for 4 years discounted back to the present at 5 percent.