The two equations can be added to eliminate y.
... (-5x +y) + (-6x -y) = (-7) + (7)
... -11x = 0
This tells you x=0. Substituting this value into either of the other equations tells you y = 7. For example, using the first equation, you get
... 0 + y = 7
The solution is (x, y) = (0, 7).
