\[\boxed{\mathbf{4.}\mathbf{136}}\]
\[\textbf{а)}\ \frac{2}{3} = \frac{6}{9};\ \ \frac{1}{3} = \frac{3}{9}\]
\[\frac{4}{9};\ \frac{5}{9}.\]
\[\textbf{б)}\ - \frac{8}{9} = - \frac{24}{27};\ \ \ - \frac{7}{9} = - \frac{21}{27}\]
\[- \frac{22}{27};\ - \frac{23}{27}.\]
\[\textbf{в)}\ \ 2,13;\ \ \ 2,12\]
\[2,121;2,125.\]
\[\textbf{г)} - 3,18;\ \ - 3,17\ \]
\[- 3,171;\ - 3,174.\]