\[\boxed{\text{5.340.}}\]
\[\textbf{а)}\ 7\frac{8}{9} - 3\frac{5}{9} = 4\frac{3}{9} = 4\frac{1}{3}\ \]
\[\textbf{б)}\ 5\frac{5}{12} + 2\frac{1}{12} = 7\frac{6}{12} = 7\frac{1}{2}\ \]
\[\textbf{в)}\ 29\frac{11}{21} - 29\frac{5}{21} = \frac{6}{21} = \frac{2}{7}\ \]
\[\textbf{г)}\ 6\frac{3}{10} + 7\frac{5}{10} = 13\frac{8}{10} = 13\frac{4}{5}\ \]