You need to just use algebra and realize the 2 questions are related to each other
You will end up getting
4x-8y-5x-3y=30
9x+21y-2x-18y=12
-x-11y=30 Multiply by 7
7x+3y=12
-7x-77y=210
7x+3y=12
Add them together
-74y=222
Divide both sides by -74
Y = -3
Plug y back into one of the equations
7x+3(-3) = 12
7x-9=12
7x=21
x=3
So, x=3 and y= -3