Multi-Variable Calculus Question

[Kirobaito]

@ = my computer symbol for partial

Okay.

"The material for constructing the base of an open box costs 1.5 times as much per unit area as the material to construct the sides. For a fixed amount of money C, find the dimensions of the box of largest volume that can be built."

V = xyz
C = 1.5xy + 2xz + 2yz
^ derived to
z = (C-1.5xy)/(2x+2y)

I've already found @V/@x and @V/@y, and x = y, as expected. However, I cannot for the life of me find out how to get x or y in terms of C, which I assume is what the problem is asking for.

Help?