Need help figuring this one out!

A cylindrical barrel is to be constructed to hold $\displaystyle 5\pi$ cubic feet of liquid. What are the dimensions of the barrel that minimize the amount of material used in it's construction?

I know that $\displaystyle Volume = \pi * r^2 * h$ and $\displaystyle SA = 2 \pi r^2 + 2 \pi r h $

So i started out trying to find h : $\displaystyle h = 5/r^2 $ (Got this from calculating $\displaystyle h = 5\pi / \pi r^2 $ from the Volume definition)

Then I used the Area calculation : $\displaystyle 2 \pi r^2 + 2 \pi r (5/r^2) $

Which turns out to : $\displaystyle A = 2\pi r^2 + 10 \pi / r$

This is where I become lost on what to do next. Any help would be appreciated!