\[\boxed{\text{4.\ 339}}\]
\[\textbf{а)}\ \frac{3}{4} \rightarrow - \frac{3}{4};\frac{4}{3}\]
\[\textbf{б)} - \frac{5}{9} \rightarrow \frac{5}{9};\ - \frac{9}{5}\]
\[\textbf{в)}\ 15 \rightarrow - 15;\frac{1}{15}\]
\[\textbf{г)} - 9 \rightarrow 9;\ - \frac{1}{9}\]
\[\textbf{д)}\ 3\frac{1}{12} = \frac{37}{12} \rightarrow - 3\frac{1}{12};\ \ \frac{12}{37}\]
\[\textbf{е)} - 4\frac{3}{8} = - \frac{35}{8} \rightarrow 4\frac{3}{8};\ - \frac{8}{35}\]
\[\textbf{ж)} - 3,4 = - \frac{34}{10} = - \frac{17}{5} \rightarrow 3,4;\ \]
\[- \frac{5}{17}\]
\[\textbf{з)}\ 12,5 = \frac{125}{10} = \frac{25}{2} \rightarrow - 12,5;\ \frac{2}{25}\]