Elevator 1 moved up 12 feet from the ground level. Its position is labeled as +12. Elevator 2 moved down 7 feet from the ground level. Its position is labeled as . (Use the hyphen for negative such as -1)

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Which addition property is being illustrated below? (type commutative or associative) (6 + 7) + 1 = 6 + (7 + 1)

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.