\[\boxed{\text{5.\ 85}}\]
\[\textbf{а)}\ 3m + 2m + 4m = 9m\]
\[\textbf{б)}\ \frac{1}{2}a + \frac{1}{3}a - \frac{1}{6}a =\]
\[= \frac{3}{6}a + \frac{2}{6}a - \frac{1}{6}a = \frac{4}{6}a = \frac{2}{3}a\]
\[\textbf{в)}\ 0,9b - 1,3b + 0,7b =\]
\[= 1,6b - 1,3b = 0,3b\]
\[\textbf{г)}\ \frac{1}{12}m - \frac{1}{4}m - \frac{1}{3}m =\]
\[= \frac{1}{12}m - \frac{3}{12}m - \frac{4}{12}m =\]
\[= \frac{1}{12}m - \frac{7}{12}m =\]
\[= - \frac{6}{12}m = - \frac{1}{2}m\]
\[\textbf{д)}\ x - 0,2x - 0,7x = x - 0,9x =\]
\[= 0,1x\]
\[\textbf{е)}\ c - 0,8c - \frac{1}{5}c - \frac{1}{2}c =\]
\[= 0,2c - 0,2c - 0,5c = - 0,5c\]