A box with a square base and open top must have a volume of 70304cm^3. We wish to find the dimensions of the box that minimize the amount of material used.

First, find a formula for the surface area of the box in terms of only x, the length of one side of the square base. A(x)=____

Then find the derivative A'(x)=_____

The critical value is x=____

Choose the correct option:

the function is increasing/decreasing until the critical value, and increasing/decreasing after, so the critical value corresponds to a local maximum/minimum.