(Compound annuity) What is the accumulated sum of each of the following streams of payments? a. $490 a year for 9 years compounded annually at 10 percent. b. $108 a year for 6 years compounded annually at 8 percent. c. $33 a year for 13 years compounded annually at 12 percent. d. $21 a year for 5 years compounded annually at 6 percent