a) The independent variable is r, the radius. You can use any allowable number for r. The dependent variable is V, the volume. Once you choose a value for r, the value of V will depend on that value of r.
b) The domain is all real numbers greater than 0. A radius cannot be zero or a negative number.
c) The output of V(8) is the function V(r) evaluated at r = 8, so it is the volume of a sphere of radius 8 units.
