What is the slope of a line that passes through (2, 1) and (2, -3)

Ineed if you could explain and give me the answer you! this needs done

Given the two similar triangles, how do i find the missing length? if a=4, b=5, and b'=7.5 find a'

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.