\[\frac{5n - 10}{n^{2} + 8n + 16}\ :\frac{4 - n^{2}}{n + 4} =\]
\[= \frac{5(n - 2)(n + 4)}{(n + 4)^{2}(2 - n)(2 + n)} =\]
\[= - \frac{5}{(n + 4)(n + 2)}.\]