Julie figures that she will need at least 540 marks to get the items she wants when visiting germany. give an estimating example of how julie could guarantee herself of having at least 540 marks. show and explain your example below.

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.