\[b_{3} = 36;\ \ b_{6} = \frac{1}{6}:\]
\[\left\{ \begin{matrix} b_{1}q^{2} = 36 \\ b_{1}q^{5} = \frac{1}{6}\text{\ \ } \\ \end{matrix} \right.\ \]
\[q^{3} = \frac{1}{36 \cdot 6}\text{\ \ }\]
\[q^{3} = \frac{1}{6^{3}}\ \]
\[q = \frac{1}{6}.\]
\[b_{1} = \frac{36 \cdot 36}{1} = 1296.\]
\[S_{4} = \frac{1296 \cdot \left( \frac{1}{1296} - 1 \right)}{\frac{1}{6} - 1} =\]
\[= \frac{1296 \cdot \left( - \frac{1295}{1296} \right)}{- \frac{5}{6}} =\]