Constructing an Open Box: An open box with a square base is requried to have a volume of 10 cubic feet.

a) Express the amount A of material used to make such a box as a function of the length x of a side of the square base. MY answer: S=x^2 + 4x(10/x^2)

b)How much material is required for a base 1 foot by 1 foot?

c)How much material is required for a base 2 feet by 2 feet?

d) Graph A=A(x). For what value of x is A smallest?

I cannot figure out b,c,d...thank you