The formula of the volume of a sphere is 4/3(πr^3). Radius is 1/2 the diameter so if the diameter is 18, the radius is 9. Now we plug that into the formula 4/3(π9^3). Now we solve for the volume step by step. First 9^3 = 729. Now 4/3(729π). Now divide 729 by 3 and multiply by 4 so 4(729/3) = 972π. The volume of the sphere is 972π.