The volume of a cylinder is given by the product of the area of its base and its height. The base of a cylinder is a disk which means that its area is given by:
Where r is the radius of the base. Here we have the diameter of the base which is two times its radius. Then the radius of the base is:
Then the area of the base is:
Now that we have the area of the base we just need to multiply it by the height:
Then the answer is 216 in³.