On a March day the temperature changed by an average of -0.5° C per hour from its high of 5° C at 1:00 pm. What was the temperature at 10:00 pm?

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.