\[\boxed{\text{4.\ 343}}\]
\[\textbf{а)}\ \frac{3}{5}\ :\left( - \frac{11}{15} \right) = - \frac{3}{5} \cdot \frac{15}{11} = \frac{- 9}{11}\]
\[\textbf{б)}\ 0,56\ :0,8 = \frac{56}{80} = \frac{7}{10}\]
\[\textbf{в)} - 0,45\ :( - 0,15) = 45\ :15 =\]
\[= 3 = \frac{3}{1}\]
\[\textbf{г)} - \frac{1}{7}\ :0,7 = - \frac{1}{7}\ :\frac{7}{10} =\]
\[= - \frac{1}{7} \cdot \frac{10}{7} = \frac{- 10}{49}\]