The science department buys microscopes every 5 years, safety goggles every 4 years, and test tubes every 2 years. they bought all three items this year. in how many years will they have to buy all three items again.

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.