Explanation:
the volume of a cylinder (as for any other regular shape that had the same top area as base area) is
base area × height
the base area of a cylinder is a circle, so the area is
pi×r²
with r being the radius (remember, the radius is half of the diameter). in our case therefore 7/2 = 3.5 yd
so, we get for the volume here
pi×3.5² × 12 = pi×12.25 × 12 = 147×pi yd³