4) \(\frac{2x-2y}{y}\cdot\frac{3y^2}{x^2-y^2}=\)

Разложим на множители: \(2x-2y=2(x-y)\), \(x^2-y^2=(x-y)(x+y)\).

\[\frac{2(x-y)}{y}\cdot\frac{3y^2}{(x-y)(x+y)}=\frac{6y}{x+y}.\]

Ограничения: \(y\ne 0\), \(x\ne y\), \(x\ne -y\).

Ответ: \(\frac{6y}{x+y}\).