\[3m^{4}n = - 2;\ \ \ m^{4}n = - \frac{2}{3}:\]
\[3m^{8}n^{2} = 3 \cdot \left( - \frac{2}{3} \right)^{2} = \frac{3 \cdot 4}{9} =\]
\[= \frac{1 \cdot 4}{3} = \frac{4}{3} = 1\frac{1}{3}\]