You can put this solution on YOUR website!
Notice we have a common term of (y+9). If we let w=(y+9) we can rewrite the equation as
So we can subtract like terms. For instance if we let x=15 it would look like
However, we don't know x, so we have to leave it alone. There are x terms of w and -11 w's, so we get
And if we replaced w with (y+9) we get
Hope this makes sense.