Need help fast don't know what to do

Aflower has 26 chromosomes. to create a new flower,how many would a sperm cell have what is called?

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.

How is this equation completed? i cannot find any examples in the book.