juan has $500 in his bank account. At the end of each month he plans to deposit $75. If these are his only transactions, which expression could be used to show the amount of money Juan will have in his account after m months?

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.