A chemist ran out of a 72 ml solution of 12% alcohol. All that is left in the lab is 8% alcohol and 20% alcohol. How many ml of 8% and 20% would be needed to make a 72 ml solution of 12%?

This is what I have so far.

.12 X 72=8.64

.08x + .2y=8.64

(100) .08x + .2y=8.64 (100)

8x + 20y= 864

Any help in solving it would be appreciated. I am at a dead end.