5. Simplify: $\frac{\sqrt{3}+\sqrt{5}}{3-\sqrt{6}-\sqrt{10}+\sqrt{15}}$.
```
Divide the denominator into two groups to get
\[
\begin{array}{l}
(3+\sqrt{15})-(\sqrt{6}+\sqrt{10}) \\
=(\sqrt{3}+\sqrt{5})(\sqrt{3}-\sqrt{2}) \text {. Answer: } \sqrt{3}+\sqrt{2} .
\end{array}
\]
```