(Compound annuity) What is the accumulated sum of each of the following streams of payments? a. $480 a year for 8 years compounded annually at 9 percent. b. $100 a year for 6 years compounded annually at 8 percent. c. $37 a year for 11 years compounded annually at 12 percent. d. \$27 a year for 4 years compounded annually at 6 percent