15. Problem 5.15 (Present Value of an Annuity) Find the present values of these ordinary annuities. Discounting occurs once a year. Do not round intermediate calculations. Round your answers to the nearest cent. a. $500 per year for 12 years at 16%. $ b. $250 per year for 6 years at 8%. $ c. $400 per year for 6 years at 0%. $ d. Rework previous parts assuming they are annuities due. Present value of $500 per year for 12 years at 16% : $ Present value of $250 per year for 6 years at 8% : $ Present value of $400 per year for 6 years at 0% : $