Hello all, I need help with my calculus. I am having a hard time with finding maximums and minimums of rectangular prisms. Does anybody think they could help me?

Question

anonymous · Answer

Max and mins are all about finding when is the first derivative zero.

anonymous · Answer

Let me give you an example: A box with a rectangular base is to be constructed of material costing $2/inch^2 for the sides and the bottom, and $3/inch^2 for the top. If the volum is 1215 inches^3 and the length is twice the width, which dimensions minimize cost.

anonymous · Answer

I understand that I have "l=2w" and "l*w*h=1215" so "3w*h=1215" but I don't know how to eliminate h or w.