An just finished taking statistics, and wants to do a survey on the average salary of Spring 2019 HCC graduates. She calculates that the standard error of the mean is $128.13 after she surveyed a group of students who reported an annual income of $43,650 and she knows the population standard deviation is $2,050, how many students were randomly sampled by An?

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.