\[\boxed{\text{4.\ 352}}\]
\[\textbf{а)}\ a = - 2;\ \ c = - 3:\]
\[2a - 3|c - 2| =\]
\[= 2 \cdot ( - 2) - 3| - 3 - 2| =\]
\[= - 4 - 3 \cdot 5 = - 4 - 15 = - 19.\]
\[\textbf{б)}\ m = - 1;n = - 2:\]
\[3m - 8|n - 4| =\]
\[= 3 \cdot ( - 1) - 8| - 2 - 4| =\]
\[= - 3 - 8 \cdot 6 = - 3 - 48 = - 51.\]