\[\boxed{\mathbf{830\ (830).\ }Еуроки\ - \ ДЗ\ без\ мороки}\]
\[18,\ 12,\ 8,\ \ldots\]
\[q = \frac{12}{18} = \frac{2}{3};\]
\[b_{6} = b_{1} \cdot q^{5} = 18 \cdot \left( \frac{2}{3} \right)^{5} =\]
\[= \frac{18 \cdot 32}{243} = \frac{64}{27}.\]
\[Ответ:q = \frac{2}{3};\ \ \ b_{6} = \frac{64}{27}.\]