I need to find the height of a cone. I have the volume and radius's. So I need to get h out of the formula.

V= pi/h(R^2+R/r+r^2)
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3

If you want to find h, you can directly substitute the values that you've already got into the formule and work with the numbers only :)

But if you absolutely want to make h the subject of formula, multiply both sides by 3.