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(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. $500 a year for 10 years discounted back to the present at 10 percent. a. What is the present value of $2,500 a year for 10 years discounted back to the present at 7 percent? (Round to the nearest cent.)