2. The solution to this question uses the same time and distance formulas. In part one, we asked where the times added up to 10. This time, we wonder when the times are equal.

Mathematica solves this equation with the following code

We get two solutions. The first is trivial. If the well has no depth, the coin takes no time to fall, and the sound takes no time to return. The second is more interesting. A depth of 23, 591 meters is the other solution. This is a very deep well indeed, almost 15 miles!!!