What equation represents the estimated population after t years?

What is the measure of the smallest angle in the diagram? 15 29 32 45

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.

Type the correct answer in the box. use numerals instead of words. if necessary, use / for the fraction bar.