How much money can be withdrawn at the end of the investment period if: a. $4,000 is invested at the end of each of 3 years at 5%/year compounded annually, with the lump sum then shifted into an investment paying 8%/year for 5 additional years? b. $12,000 is invested at the end of each of 10 years at 10%/year compounded annually, with the lump sum then shifted into an investment paying 5%/year for 3 additional years? c. $18,000 is invested at the end of each of 5 years at 9%/year compounded annually, with the lump sum then shifted into an investment paying 7%/year for 8 additional years?