\[\frac{\sqrt{10} - \sqrt{6}}{\sqrt{40} - \sqrt{30} - \sqrt{24} + \sqrt{18}} =\]
\[= \frac{\sqrt{10} - \sqrt{6}}{2\sqrt{10} - \sqrt{3} \cdot \sqrt{10} - 2\sqrt{6} + \sqrt{3} \cdot \sqrt{6}} =\]
\[= \frac{\sqrt{10} - \sqrt{6}}{\sqrt{10}\left( 2 - \sqrt{3} \right) - \sqrt{6}\left( 2 - \sqrt{3} \right)} =\]