\[\boxed{\text{4.\ 175}}\]
\[a + c + ( - 11)\]
\[\textbf{а)}\ a = - 23;c = - 48:\]
\[- 23 + ( - 48) + ( - 11) =\]
\[= - (23 + 48 + 11) = - 82.\ \]
\[\textbf{б)}\ a = - 51;c = - 72:\]
\[- 51 + ( - 72) + ( - 11) =\]
\[= - (51 + 72 + 11) = - 134.\]
\[\textbf{в)}\ a = - 34;c = - 25:\]
\[- 34 + ( - 25) + ( - 11) =\]
\[= - (34 + 25 + 11) = - 70.\]
\[\textbf{г)}\ a = - 2,3;c = - 8,7:\]
\[- 2,3 + ( - 8,7) + ( - 11) =\]
\[= - 11 + ( - 11) = - 22.\]