Originally Posted by

**Rumor** At least, I think that's what this question is asking for.

"The total cost to build an open box with a constant volume V and with a square base is given by the function

$\displaystyle C(x)=10x^2+\frac{60V}{x}$

where x is the length of the square base.

a) Find the value of x that will produce the box with the minimum total cost. Your answer will involve the parameter of V.

b) Verify that this value of x will give the local minimum.

c) Give an argument based on calculus why this value of x actually gives a global minimum, not just a local minimum."

I'm not sure how to start.

Any help, please?