$$\frac{x^2 - y^2}{3x - 2x^2 + 3y - 2xy} = \frac{(x-y)(x+y)}{3(x+y) - 2x(x+y)} = \frac{(x-y)(x+y)}{(x+y)(3-2x)} = \frac{x-y}{3-2x}$$