\[\boxed{\mathbf{4.}\mathbf{112}}\]
\[\textbf{а)}\ a = - 63,6;c = 61,9:\]
\[|a| + |c| = | - 63,6| + |61,9| =\]
\[= 63,6 + 61,9 = 125,5.\]
\[\textbf{б)}\ a = - 73,2;\ \ c = - 5,8:\]
\[|a| - |c| = | - 73,2| - |5,8| =\]
\[= 73,2 - 5,8 = 67,4.\ \]