6) $$ \frac{8m}{n} : \frac{4m}{n} = \frac{8m}{n} \cdot \frac{n}{4m} = \frac{8mn}{4mn} = \frac{8}{4} \cdot \frac{m}{m} \cdot \frac{n}{n} = 2 \cdot 1 \cdot 1 = 2 $$
Ответ: 2