The Two Towers Problem is easily generalized in several ways beyond the version found in Stewart. For example:
Clearly, all the solutions presented in this article will still apply.
In addition, you or your students may suggest other problem solving avenues, such as equating the slopes of the segments PR and RT'.
Here again is the link from page 2 to other familiar optimization problems that would serve to illustrate various solution techniques that are accessible at each of the four levels of the framework.
Some examples of other easily accessible optimization problems
You may know these problems as