To solve for r, you just need to isolate r. To do that, divide by h and π on both sides:
[tex] \frac{V}{h \pi }=r^2 [/tex]
Then, square root both sides to get rid of the 'squared':
[tex]r = \sqrt{ \frac{V}{h \pi } } [/tex]
Or, if you wanted the answer in terms of π, then just don't divide by it, just divide by h and then square root it.
