\[\frac{y^{2} + 2y}{y^{2} - 4y + 4} - \frac{4y}{y^{2} - 4y + 4} =\]
\[= \frac{y^{2} - 2y}{(y - 2)²} = \frac{y(y - 2)}{(y - 2)^{2}} = \frac{y}{y - 2}\]