\[\boxed{\text{5.\ 47}}\]
\[\textbf{а)}\ ( - m - n) + ( - a + n) =\]
\[= - m - n - a + n = - m - a\]
\[\textbf{б)}\ ( - a + c) + ( - d - c) =\]
\[= - a + c - d - c = - a - d\]
\[\textbf{в)}\ ( - a - c) + (a + c) =\]
\[= - a - c + a + c = 0\]