i am not sure what you mean by 7ft, but i am going to assume that the radius of the sphere is 7 feet.
the volume of a sphere - 4/3 * π * r^3
plugging in the 7 feet as the radius and 3.14 as π, you get:
4/3 * 3.14 * 343
which equals
≈ 1436.03
i hope this helped! please correct me if i'm wrong :)