\[\boxed{\text{6.289.}}\]
\[\textbf{а)}\ 66,6\ :6 = 11,1\ \]
\[\textbf{б)}\ 6,66\ :6 = 1,11\ \]
\[\textbf{в)}\ 3\ :5 = 0,6\ \]
\[\textbf{г)}\ \frac{4}{5} = 0,8\ \]
\[\textbf{д)}\ \frac{1,8}{3} = 1,8\ :3 = 0,6\ \]
\[\textbf{е)}\ \frac{3,6}{4} = 3,6\ :4 = 0,9\ \]
\[\textbf{ж)}\ 0,56\ :9 = \frac{56}{100} \cdot \frac{1}{9} = \frac{14}{25} \cdot \frac{1}{9} =\]
\[= \frac{14}{225}\]
\[\textbf{з)}\ 0,42\ :6 = 0,07\ \]
\[\textbf{и)}\ 37,8\ :10 = 3,78\ \]
\[к)\ \frac{5,1}{10} = 5,1\ :10 = 0,51\ \]
\[л)\ 47\ :100 = 0,47\ \]
\[м)\ 27,3\ :10\ 000 = 0,00273\ \ \]