I would use the process of elimination. Divide 13 from both sides
2x+7y=-57 y=-7 then plug in y to an equation
-6x-8y=80 2x+7(-7)=-57 multiple
multiple the first equation by 3 2x-49=-57 add 49 to both sides
6x+21y=-171 2x=-8 divide two from both sides
-6x-8y=80 x=-4
combine like terms So your things would be x=-4 and y=-7
13y=-91 And itd make the solution (-4,-7).