You have a babysitting job that pays $6 an hour. You also have cashier job that pays $9 an hour. You don't want to work more
than 20 hours a week, but you want to make at least $150 a
week. What are the number of hours you can work at each job
and still make at least $150 a week?

Set $r$ is a set of rectangles such that (1) only the grid points shown here are used as vertices, (2) all sides are vertical or horizontal and (3) no two rectangles in the set are congruent. if $r$ contains the maximum possible number of rectangles given these conditions, what fraction of the rectangles in set $r$ are squares? express your answer as a common fraction.