\[\boxed{\text{4.\ 311}}\]
\[\textbf{а)}\ 5,6\ :\left( - 1\frac{3}{4} \right) = - \frac{56}{10}\ :\frac{7}{4} =\]
\[= - \frac{28}{5} \cdot \frac{4}{7} = - \frac{16}{5} = - 3,2\]
\[\textbf{б)} - \frac{4}{5}\ :( - 0,3) = \frac{4}{5}\ :\frac{3}{10} =\]
\[= \frac{4}{5} \cdot \frac{10}{3} = \frac{4 \cdot 2}{3} = \frac{8}{3} = 2\frac{2}{3}\]
\[\textbf{в)} - 4,8\ :1\frac{3}{5} = - 4,8\ :1,6 =\]
\[= - 48\ :16 = - 3\]
\[\textbf{г)}\ 1,3\ :\left( - \frac{1}{4} \right) = - \frac{13}{10} \cdot 4 =\]
\[= \frac{- 52}{10} = - 5,2\]