Ok so 6x - 3y = -21
And 4x = 3y - 9
From the second equation, 4x - 3y = -9
So if you subtract the second from the first,
(6x-3y) - (4x-3y) = -21 - (-9)
So 2x = -12
x = -6
Now we know x=-6, and you can sub it back into any equation:
6(-6) -3y = -21
-36 - 3y = -21
-3y = 15
y = -5
So x=-6 and y=-5
Hope this helps
