The formula of the volume of the cylinder is

Where:
r is the radius of its base
h is its height
Since the radius is 1/2 the diameter
Since the diameter of the base is 8 ft, then

Since the height is 12 ft, then
h = 12
Substitute r by 4 and h by 12 in the formula above to find the volume

Round it to the nearest whole number
V = 603 cubic feet to the nearest whole number