Question

Square corners are cut from a piece of cardboard 40c by 25cm and the edges are turned up to form an open box. what size squares must be removed to make a box of maximum volume?
I have this so far:
v=length x width x depth
v=(40-25x)^2 x x
v=(80-160+50x^2) x x
v=80x-160x^2+50x^3
--- not sure about the 50x^3

then
v'(x)=80-320x+150x^2
---got stuck here

Answer 1

correction-> 40cm