let's recall that a Centroid in a triangle cuts the Medians into a 2:1 ratio, or namely CG : GD are in a 2: 1 ratio, we can also look at it that the side CD is 2/3 of CD whilst GD is 1/3 of CD, so

Answer: 9 inches
Explaination: The volume of a cylinder, V = (πr^2)H, so H = V/(πr^2).
Using the parameters you specified, H = 324π/[(π)(6^2)] = 324π/36π = 324/36 = 9 inches
The answer is D and it's pretty simple to do: