\[\boxed{\mathbf{2.}\mathbf{128}}\]
\[\textbf{а)}\ 31\ :9 = \frac{31}{9} = 3\frac{4}{9}\]
\[\textbf{б)}\ 81\ :9 = \frac{81}{9} = 9\]
\[\textbf{в)}\ 402\ :15 = \frac{402}{15} = 26\frac{12}{15} =\]
\[= 26\frac{4}{5}\]
\[\textbf{г)}\ 1429\ :14 = 102\frac{1}{14}\]