The volume of a cylinder is 540π ft3. the height is 15 ft. what is the diameter of the cylinder?

 
In this case, we want to solve for r. Once we have the radius we can multiply it by 2 and get the diameter. 

So let's plug things in that we know:


First, divide both sides by 15.


Now, divide both sides by  (3.14)


Now we have to take the square root of both sides to find the radius.
3.39=r

The last step is to multiply the radius by 2 to get the diameter.
2r=6.78

The diameter is 6.78

Hope this helps.