What is the exact volume of a sphere that has a radius of 7.5 ft?
ft^3

The volume of a sphere is 4/3 * pi * radius^3. So the equation is 4/3 * pi * 7.5^3. First of all, 7.5^3 = 421.875. Then you 4/3 * pi * 421.875. 4/3 * 421.875 = 562.5. Then you do 562.5 x pi.
If you use pi as 3.14, then the answer is 1766.25.
If you use pi as 3.14159, then the answer is 1767.144375.
If you're crazy and use pi as 3.141592653589793238462643383279502884197 then the answer is roughly 1767.145867644259.
Hope I helped! :)