You put $20,000 on deposit on your thirtieth birthday at 5 percent compounded annually. On your fortieth birthday, the account begins earning 6 percent. Then on your fiftieth birthday, it begins earning 7 percent. You plan to withdraw equal annual amounts on your sixty-first, sixty-second, . . . , seventieth birthdays. a. How much will be your annual withdrawal? b. On your sixty-fifth birthday, you decide to withdraw the entire amount remaining. How much do you withdraw?