\[\boxed{\mathbf{4.}\mathbf{40}}\]
\[\textbf{а)} - n = - 2;\ - n = 16;\ - n = 0.\]
\[\textbf{б)}\ a = - 38;\ \ a = 17;\ \ a = - 1,7;\ \ \]
\[a = 14,5;\ \ \ a = - 230;\]
\[a = 140;\ \ \ a = - \frac{9}{11};\ \ \ a = \frac{14}{17};\ \ \ \]
\[a = - 5\frac{3}{4}.\]
\[\textbf{в)} - ( - m) = m:\]
\[m = 41;\ \ m = - 3,6;\ \ m = 0;\ \ \]
\[m = - 2\frac{9}{35};\ \ m = \frac{8}{9}\text{.\ }\]