487 2) 5m 15m³ m²-n2m-n

2) $$ \frac{5m}{m^2-n^2} : \frac{15m^3}{m-n} = \frac{5m}{(m-n)(m+n)} \cdot \frac{m-n}{15m^3} = \frac{5m(m-n)}{(m-n)(m+n)15m^3} = \frac{5m}{15m^3(m+n)} = \frac{1}{3m^2(m+n)} $$

Ответ: $$ \frac{1}{3m^2(m+n)} $$