Related Rates - Inflating Spherical Balloon

You are inflating a spherical balloon at the rate of 7 𝑐𝑚3/𝑠. How fast is its radius increasing when the radius is 4 cm?

[justinpeabody]

The interesting thing about this type of problem is that if you were to use the differentiated equation to find some dr/dt values after the radius has increased beyond 4 cm, you would find that the radius increases at a slower and slower rate as time passes, provided that it is being inflated at a constant rate.