2x+6y=-12 divide everything by 2 → x + 3y = -6
5x-5y=10 divide everything by -5 → - x + y = -2
Notice, Paypay, that if we just add these last two together, we have :
4y = - 8 divide by 4 on both sides
y = -2
And using -x + y = -2 → -x - 2 = -2 so x = 0
