\[18;6;2\ldots\ \ \ \ \]
\[b_{1} = 18;\ \ q = \frac{6}{18} = \frac{1}{3}\]
\[b_{6} = b_{1} \cdot q^{5} = 18 \cdot \left( \frac{1}{3} \right)^{5} = \frac{18}{3^{5}} =\]
\[= \frac{2}{27}\]
\[Ответ:\frac{2}{27}.\]