3) \frac{6x-30}{x+8}:\frac{x^{2}-25}{2x+16};

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

Ответ: $$\frac{12}{x+5}$$