-77x - 78x = -155x
-66y - (-66y) = -66y + 66y = 0
264 - (-666) = 264 + 666 = 930
This leaves us with -155x = 930. Dividing by -155 on both sides, we find:
x = -6
Substitute x = -6 into one of the two original equations, solve for y, and then state the full solution to the system of equations.