3x-6y=12
+
2x+6y=-12
_________
5x=0
x=0
(Since the y's already canceled each other, I didn't have to multiply anything.)
Now plug the x-value in both equation and see if it works:
3(0)-6y=12
-6y=12
y=-2
2(0)+6y=-12
6y=-12
y=-2
So the answer is (0,-2)