4) \frac{3m}{16n^2} \cdot 8n^6

4) \frac{3m}{16n^2} \cdot 8n^6 = \frac{3m \cdot 8n^6}{16n^2} = \frac{24mn^6}{16n^2} = \frac{3mn^4}{2}

Ответ: \frac{3mn^4}{2}