There's a box with 16 cubic meter volume. Height z, depth y, width x. The sides cost $10/sq meter and top and bottom cost $20/sq meter. Write an equation for the cost (C) of the box using x and y.
I'm bad at coming up with formulas, is there a general procedure or any places where I should start?
and I think I should add them so cost=sides+front/back+top/bottom
This won't work so well as I have no clue how to incorporate the volume and I'm not allowed to use z.