Each time Kendra walks Mr. Karl's dog, he gives her $3. Kendra walks the dog for 30 minutes. If she walks the dog on Monday, Tuesday, and Thursday, how much money does Kendra make each week for walking Mr. Karl's dog?

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.