2x^2-18y^2/3y-x
2x^2 - 18y^2
_________________ Factor the numerator
3y - x
2 (x^2 - 9y^2)
________________
3y - x
2 (x + 3y)(x - 3y)
____________________
3y - x
-2 (x + 3y)(-x + 3y)
_______________________
3y - x
-2 (x + 3y)(3y - x)
_______________________
3y - x
-2 (x + 3y)