so find a common lets use 2 on the top
2x-4y=30
2x+4y=-18, now we have 4x=12, x=3
so lets substitute, lts use the top
3-2y=15
-2y=12
y=-6
im not sure x could be 12 i would try plugging each one them into the equation and see with one balances out
the other one is x=12, y=-3/2
