\[\boxed{\text{4.\ 341}}\]
\[\textbf{а)} - \frac{7}{9} + \frac{5}{18} = - \frac{14}{18} + \frac{5}{18} =\]
\[= - \frac{9}{18} = \frac{- 1}{2}\]
\[\textbf{б)}\ 2\frac{4}{13} - 1\frac{11}{26} = 1\frac{17}{13} - 1\frac{11}{26} =\]
\[= \frac{34}{26} - \frac{11}{26} = \frac{23}{26}\]
\[\textbf{в)}\ \frac{5}{8} - \frac{7}{16} = \frac{10}{16} - \frac{7}{16} = \frac{3}{16}\]
\[\textbf{г)}\ 1,3 - 4,5 = - 3,2 = - \frac{32}{10} =\]
\[= \frac{- 16}{5}\]