Change in Volume of Balloon

A spherical balloon is inflated until it reaches a radius of 7 cm. The volume of a sphere can be calculated using the formula: $$V = \f\frac{4}{3} \pi r^3$$ where $r$ is the radius. If the balloon is then released and the radius of the balloon decreases uniformly to 3 cm, what is the change in volume of the balloon during this process?

To solve for the change in volume, first calculate the volume at both the initial and final radii, and then find the difference between them.