A bank has three different types of account in which the interest rate depends on the amount invested. The ordinary account offers a return of 6% and is available to every customer. The extra account offers 7% and is available only to customers with $5000 or more to invest. The superextra account offers 8% and is available only to customers with $20 000 or more to invest. In each case, interest is compounded annually and is added to the investment at the end of the year. A person saves $4000 at the beginning of each year for 25 years. Calculate the total amount saved on the assumption