\[\boxed{\mathbf{905\ (905).\ }Еуроки\ - \ ДЗ\ без\ мороки}\]
\[S = - 60;\ \ b_{1} = - 65\]
\[S = \frac{b_{1}}{1 - q}\ \]
\[1 - q = \frac{b_{1}}{S} = \frac{- 65}{- 60} = \frac{13}{12}\text{\ \ }\]
\[q = 1 - \frac{13}{12} = - \frac{1}{12}\]
\[Ответ:\ q = - \frac{1}{12}.\]