Question

Measuring the volume of a ball that is 24cm across how can you set up an equation

Answer 1

The volume of every sphere is

           Volume = (4/3) (pi) (radius)³

When you say "across", I think you mean the diameter of the ball.
The radius is half of the diameter = 12 inches.

         Volume = (4/3) (pi) (12 inches)³

                       = (4/3) (pi) (1,728 cubic inches)

                       =    7,238.2 cubic inches .  (rounded)