\[\frac{6x - 30}{x + 8}\ \ :\frac{x^{2} - 25}{2x + 16} =\]
\[= \frac{6 \cdot (x - 5)}{x + 8}\ \ :\frac{(x - 5)(x + 5)}{2 \cdot (x + 8)} =\]
\[= \frac{6 \cdot (x - 5) \cdot 2 \cdot (x + 8)}{(x + 8)(x - 5)(x + 5)} = \frac{12}{x + 5}\]