I was having trouble with the last question (in the title), so I went to the solutions PDF and found a bunch of typos. I sorta drew it out (sorry IDK how to get my drawing into here), then I got to this part:
Therefore, $\frac{YZ}{Y'Z'} = \frac{X';Y}{X'Y'}$, so if we want $Z$ to be chosen so that $YZ$ is maximal, we need to maximize $X39; Y$.
The ; then 39; really confused me, and the solution doesn't even have a diagram.
It would help if one of you guys clarified and posted a solution. Thanks.
A very nice question and solution (but with some typos unfortunately).