Dora reaches her goal of $ 400 in savings. she decide to set a new goal of $900.how many $100 bills will she need to reach $900 in savings? explain your answer using words pictures or numbers

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.