Solve the equation involving simple interest. Sherica invested in a mutual fund, and at the end of 18 yr she has $11,180 in her account. If the mutual fund returned an
average yield of 4%, how much did she originally invest?

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.