Решение задачи 1:
$$\frac{45a^4b^3}{57c^4} : \frac{15(ab)^3}{19c^2} = \frac{45a^4b^3}{57c^4} \cdot \frac{19c^2}{15a^3b^3} = \frac{45 \cdot 19}{57 \cdot 15} \cdot \frac{a^4b^3c^2}{a^3b^3c^4} = \frac{3 \cdot 1}{3 \cdot 1} \cdot \frac{a}{c^2} = \frac{a}{c^2}$$Ответ: $$\frac{a}{c^2}$$
Решение задачи 2:
$$\frac{6a-30}{3b+5} : \frac{a^2-25}{6b+10} = \frac{6(a-5)}{3b+5} \cdot \frac{2(3b+5)}{(a-5)(a+5)} = \frac{6}{1} \cdot \frac{2}{(a+5)} = \frac{12}{a+5}$$Ответ: $$\frac{12}{a+5}$$