\[\boxed{\mathbf{П.\ 9}}\]
\[= 4,2 \cdot ( - 0,9) - 15,6 \cdot 0,2 =\]
\[= - 3,78 - 3,12 = - 6,9\]
\[= - 0,52 + 0,18 \cdot ( - 0,6) =\]
\[= - 0,52 - 0,108 = - 0,628\]
\[= - \frac{108}{75} - (2,43 + 0,78) =\]
\[= - \frac{36}{25} - 3,21 = - \frac{144}{100} - 3,21 =\]
\[= - 1,44 - 3,21 = - 4,65\]
\[= - 42,42\ :7 + 3,9 \cdot 2,6 =\]
\[= - 6,06 + 10,14 = 4,08\]
\[5) - 1\frac{2}{3} \cdot \left( \frac{3}{5} \right)^{2} - 9\frac{4}{5}\ :\frac{7}{11} =\]
\[= - \frac{5}{3} \cdot \frac{9}{25} - \frac{49}{5} \cdot \frac{11}{7} =\]
\[= - \frac{3}{5} - \frac{77}{5} = - \frac{80}{5} = - 16\]
\[6) - 7,2\ :\frac{6}{11} - 12,8 \cdot \left( \frac{3}{4} \right)^{3} =\]
\[= - \frac{36}{5} \cdot \frac{11}{6} - \frac{64}{5} \cdot \frac{27}{64} =\]
\[= - \frac{66}{5} - \frac{27}{5} = - \frac{93}{5} = - 18,6\]