\[x_{3} = 6;\ \ \ x_{6} = 162:\]
\[\left\{ \begin{matrix} x_{1}q^{2} = 6\ \ \ \ \\ x_{1}q^{5} = 162 \\ \end{matrix}\text{\ \ \ \ \ \ \ \ } \right.\ \]
\[\left\{ \begin{matrix} x_{1}q^{2} = 6\ \ \ \ \ \ \ \ \ \ \ \ \ \ \\ 4x_{1}q² \cdot q^{3} = 162 \\ \end{matrix}\text{\ \ \ \ \ } \right.\ \]
\[6 \cdot q^{3} = 162\ \ \ \ \ \]
\[q^{3} = \frac{162}{6}\]
\[q^{3} = 27\ \ \ \ \ \]
\[q = 3.\]
\[x_{1} = \frac{6}{q^{2}} = \frac{6}{9} = \frac{2}{3}.\]
\[Ответ:\ \ \frac{2}{3}.\]