I thought the formula would be .04x+.07y=660

A mother earned $13,750,00 from royalties onher cookbook sheset aside 20 % of this for a down payment on a new home. The balance will be used for her son's Future education. She invests a portion of the money in a bank certificate of deposit that earns 4% and the remainder in a savings bond that earns 7% The total interest earned after one year is 8 (0606, 00. How much money was invested at each rate