A student scheduled to graduate at age 23 is making plans to retire by age 48. He plans to begin by investing $2,400 per year ($200/month) the first year, an additional $2,640 the sec- ond year, and increase the annual amount added to the investment by 10 percent every year to $2,904 the third year, and so on. He hopes by careful management to average a 10 percent return compounded on reasonable investments. (a) How much would he accumulate by age 48 (25 years)? (b) If he could raise his average interest rate of return on the investment to 12 percent, what would the amount be by age 48? (c) How much has the annual amount required to be invested per year grown in 25 years?