\[\frac{q^{3} - q}{q^{2} - 1} = 3\]
\[\frac{q\left( q^{2} - 1 \right)}{q^{2} - 1} = 3;\ \ \ q \neq \pm 1\]
\[q = 3.\]
\[b_{1} = \frac{48}{27 - 3} = \frac{48}{24} = 2.\]
\[S_{6} = \frac{2 \cdot (729 - 1)}{2} = 728.\]
\[Ответ:728.\]