Question

If I have the height and volume of a cylinder, how do I find the radius? or diameter?

Answer 1

$V=\pi r^2h\\ r^2=\frac{V}{\pi h}\\ r=\sqrt{\frac{V}{\pi h}}$

Answer 2

If you have the volume, that's a pretty good giveaway that you ought to use
the formula for the volume of a cylinder, since it involves all the other things ...
the things you're given, and the things you need to find.  If you know the formula
for the volume of a cylinder, you can whip out the answer in a second.  If you don't
know the formula, then you are toast.

Volume of a cylinder = (pi) (radius)² (length or height)

Divide each side of the equation by (pi) x (height) and you have

(Radius)² = Volume / (pi x height)

You HAVE volume and height, so you can use this equation to calculate
the radius.  Once you have that, if you need the diameter, it's just double
the length of the radius.

That's how.