\[\frac{xy + y^{2}}{a - 3b}\ :\frac{x^{2} - y^{2}}{2a - 6b} =\]
\[= \frac{y(x + y) \cdot 2(a - 3b)}{(a - 3b)(x + y)(x - y)} =\]
\[= \frac{2y}{x - y}\]