\( \frac{m(a-b)}{3n^{2}} \cdot \frac{2m}{n(b-a)} = \frac{m(a-b)}{3n^{2}} \cdot \frac{2m}{-n(a-b)} = \frac{m \cdot 2m \cdot (a-b)}{3n^{2} \cdot (-n) \cdot (a-b)} = \frac{2m^{2}(a-b)}{-3n^{3}(a-b)} = -\frac{2m^{2}}{3n^{3}} \)Ответ: $$-\frac{2m^{2}}{3n^{3}}$$