Derrick is trying to save money for the down payment on a used car. His parents have said that, in an effort to help him put aside money, they will pay him 10% interest on the money Derrick accumulates each month. At the moment, he has saved $500. Suppose Derrick does not add any money to the savings. Write a recursive function rule that model the money Derrick will accumulate with only the addition of the interest his parents pay.