Which graph represents a function?

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

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

7. the area of the playing surface at the olympic stadium in beijing isof a hectare. what area will it occupy on a plan drawn to a scaleof 1: 500?