\[\frac{2}{3x + 6} + \frac{x^{2} - x - 3}{x^{2} - 4} - 1 =\]
\[= \frac{2x - 4 - 3x + 3}{3\left( x^{2} - 4 \right)} =\]
\[= \frac{- x - 1}{3\left( x^{2} - 4 \right)} =\]
\[= \frac{x + 1}{3 \cdot (4 - x^{2})}\]