An amphitheatre has 20 seats in the first row, 22 in the second, 24 in the third, and so on, for 33 rows how many seats are in the amphitheatre

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.