On a standardized exam, the scores are normally distributed with a mean of 79 and a standard deviation of 20. Find the z-score of a person who scored 121 on the exam.

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.