You didn't give the box plot, but to obtain the percentage of people between 20 and 37 years old, first of all, find the total number of people, T. Next, find the total number of people between 20 and 37 years old, t.
A lot of teachers don't teach SohCahToa anymore! this acronym will really help you. I'd suggest looking up how to use it, it'll make trigonometry WAY easier!