In order to solve the following system of equations by addition, which of the following could you do before adding the equations so that one variable will be eliminated when you add them?
4x-2y=7
3x-3y=15
A.Multiply the top equation by 3 and the bottom equation by 4
B.Multiply the top equation by 3 and the bottom equation by 2
C.Multiply the top equation by -3 and the bottom equation by 2
D.Multiply the top equation by 1/3.