A bird flew three-fifths of a mile in one-quarter of an hour. What is this speed expressed in miles per hour?
A. 0.15
B. 0.24
C. 0.42
D. 2.4

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.