College Fund When Marcus started high school, his grandmother opened a college savings account. On the first day of each school year she deposited money into the account: $1000 in his freshman year, $600 in his sophomore year, $1100 in his junior year and $900 in his senior year. The account earns interest of r% at the end of each year. When Marcus starts college after four years, he gets the balance of the savings account plus an extra $500. a. If r is the annual interest rate of the bank account, the at the end of the year the balance in the account is multiplied by a growth factor of x=1+r. Find an expression for the total amount of money Marcus receives from his grandmother as a function of this annual growth factor x.