Mr. Black bought three 2-kilogram jars of peanut butter for school snacks. He spread the peanut butter on bagels to
feed 60 students. How many grams of peanut butter did he
use for each bagel?

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.