\[\boxed{\text{4.\ 371}}\]
\[m \cdot n = n \cdot m\]
\[\textbf{а)}\ m = - 1,5;\ \ n = 2,4:\]
\[- 1,5 \cdot 2,4 = 2,4 \cdot ( - 1,5)\]
\[- 3,6 = - 3,6\]
\[верно.\]
\[\textbf{б)}\ m = - 4\frac{1}{5};\ \ n = - 3\frac{1}{7}:\]
\[- 4\frac{1}{5} \cdot \left( - 3\frac{1}{7} \right) = - 3\frac{1}{7} \cdot \left( - 4\frac{1}{5} \right)\]
\[\frac{21}{5} \cdot \frac{22}{7} = \frac{22}{7} \cdot \frac{21}{5}\]
\[\frac{462}{35} = \frac{462}{35}\]
\[верно.\]