When there is a 20.1 mi/hr wind, an airplane can fly 630 mi with the wind in the same time that it can fly 521 mi against the wind. Find the speed of the plane when there is no wind.

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.