\[\boxed{\text{5.278.}}\]
\[\textbf{а)}\ 7 + 2\frac{5}{8} = 9\frac{5}{8}\ \]
\[\textbf{б)}\ 9\frac{1}{9} + 20 = 29\frac{1}{9}\ \]
\[\textbf{в)}\ 64\frac{1}{7} + 4\frac{4}{7} = 68\frac{5}{7}\ \]
\[\textbf{г)}\ 7\frac{5}{7} + 4\frac{1}{7} = 11\frac{6}{7}\text{\ \ }\]