This is a Mathematica file to solve Problem 68, p. 309.

Note the funny way that functions are defined: using the underscore.

But since -2 is less than zero, it's not in the domain (time must be positive). Only 2 hours is an interesting potential critical point.

This is less than zero, so we have a relative max. That's good!

So 3/4% is the maximum concentration.

Yep! Sure enough, a maximum.