-x+2y=6x-2y=-6

Question

`-x+2y=6x-2y=-6`

Answer 1

So I would start by adding the equations, -x+2y=-6 and 6x-2y=-6 this gives you 5x=-12 hence x=-12/5.
Now using -x+2y=6x-2y with x=-12/5 you get y =-21/5.
These are one set of solutions and your can test them by plugging x=-12/5 and y =-21/5 into your original long equation that you posted to see the they all give -6 as an answer!
Please let me know if you need further explanation