An 80 meter rope is suspended at its two ends from the tops of two 50 meter flagpoles. If the lowest point to which the midpoint of the rope can be pulled is 36 meters from the ground, then the distance, in meters, between the flagpoles is: A. 6√39
B. 36√13
C. 12√39
D. 18√13
E. 12√26
Please ignore the other doodles in the picture

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.