Divide the first equation by 2 and add the result to the second equation. This will eliminate x.
... (-4x -2y)/2 + (2x +4y) = (-12)/2 +(-12)
... 3y = -18 . . . . . collect terms
... y = -6 . . . . . . . divide by 3
Substitute this into either equation to find x. Let's use the second equation, where the coefficient of x is positive.
... 2x +4(-6) = -12
... 2x = 12 . . . . . . . . add 24
... x = 6 . . . . . . . . . . divide by 2
The solution is (x, y) = (6, -6).
