A sports ball is a sphere. To find the volume of a sphere, we need to use the next formula:

Where
pi = 3.141592...
r = radius
Since we have that the diameter is 15 cm, and the radius is half of this value, we have that the radius is 15/2 = 7.5 cm.
Then, applying the formula, we have:

Therefore, the volume for the sports ball with a diameter of 15 cm is V = 1767.1 cm^3 (rounded to the nearest tenth).
We have that:
4/3 = 1.333333.... = 1 + 1/3
pi = 3. 14159265358979...(for simple calculations, pi = 3. 14 or 22/7)
We raise the value of 7.5 cm to the third power, that is, (7.5cm)^3 = (7.5cm*7.5cm*7.5cm) = 421.875 cm^3.
Then, we multiply:
(4/3) * 3.1415926535 * (421.875cm^3) = 1767.14587 cm^3.
(In this case, the value for pi was very precise).