A water tank is in the shape of a right circular cylinder with a height of 20 feet and a volume of 320π cubic feet. What is the diameter, in feet, of the water tank?

The formula for volume of a cylinder is  V=π r^2 h.
So plug in,
320π=π r^2 20
solve (sadmep (opposite of pemdas))
divide pi out
320=r^2 20
divide 20 out
16=r^2
square root of 16 is 4, so the radius is 4. 
Since the 2r=d, the diameter is 8.
P.s. lol it thought I was copying an answer from online...