help me with this

Question

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%

The amount invested at 10% was

Answer 1

X+Y = 7200 ----> Y = 7200 -x

0.1X + 0.09Y = 680

10X + 9Y = 68000 <--- multiplies by 100

10x + 9(7200-x) = 68000

10x + 64800 -9x = 68000

x + 64800 = 68000

x = 3200

y = 4000