Related rates - Snowball melts, area decreases, extra Chain rule discussion (Matheno.com)

Calculus related rates problem & solution, with extended discussion of Chain rule: "A snowball symmetrically such that it is always a sphere. Its surface area decreases at the rate of .... How fast is its radius changing at the instant when r = ...?" Let's solve this together, step-by-step, and illustrate a strategy you can use to solve *every* related rates problem.