A+1.6=2.1
Can someone help me with this and can you also do the work to it that would be nice (:

Solve this system of equations. 12x − 18y = 27 4x − 6y = 10

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.

Which property was used to simplify the expression? 3c+9 +4c=3c+4c+9