First thing you need to do is isolate the height (h). Since the height is multiplying with the pi and r^2 you have to divide those from that side of the equation to make them disappear. In doing that you also have to divide them from the other side of the equation (the volume (V)).

So now:

V/(pi*r^2) = h

The radius (r) is half of the diameter. So the diameter divided by 2 equals the radius.

So now:

V/(pi*((d/2)^2)) = h

Plug in the numbers:

15/(pi*((6/2)^2)) = h

15/(pi*(3^2)) = h

15/(pi*9) = h

To simplify your answer divide both the top and bottom by a number they can both be evenly divided by (in this case it’s 3)

So 15/3 = 5 and 9/3 = 3

So your answer is:

5/(pi*3) inches or about .53 inches

15 = pi * 9 * height

thus the height is 15 / 9pi which is about 0.53