1. The problem statement, all variables and given/known data I guess I should point out that the volume was known, which is 100 cm. 3. The attempt at a solution I don't see why using the chain rule compels you to take the inverse of 4∏r^2. Any help would be appreciated. I have a feeling that the solution is something like 100 = (4pir^2)/x but that still is not right.