24. (Length of an ordinary annuity)You plan to make deposits into a retirement account and have set a goal of having $2 million in the account when you retire. You forecast you can earn interest at a 6% rate. How many years will it take for you to reach your retirement goal if, at the end of each year, you deposit:

a. $10,000? c. $30,000? b. $20,000? d.$40,000?