Solve using elimination.

-9x + 9y = 18

-6x + 9y = - 12

You can multiply either the top or bottom equation by - 1 so lets say you apply it to the bottom equation it'll look like this:

-9x + 9y = 18

6x - 9y = 12

then the + 9y and - 9y will cancel out

-9x = 18

6x = 12

then you add the two equations together

-3x = 30

divide both sides by - 3

x = - 10

x = - 10 and y = - 8