Let's solve this system thru the elimination method:
-6x-3y=3 Mult. all terms by -1 to obtain 6x+3y = -3
-6x+7y=-7 Add your result to the second equation:
6x+3y = -3
-6x+7y=-7
----------------
10y = -10, and so y = -1. Subst. -1 for y in the first equation and then solve the result for x. You'll find that x = 0.
Thus, the solution is (0, -1).