A college student earned $7200 during summer vacation working as a waiter in a restaurant on the boardwalk at the beach. The student invested part of...

A college student earned $7200 during summer vacation working as a waiter in a restaurant on the boardwalk at the beach. The student invested part of the money at 10% and the rest at 9%. If the student received a total of $680 in interest at the end of the year, how much was invested at 10%