\[b_{1} = 0,0001;\ \ \ \ \ \ \ \ b_{8} = - 1000:\]
\[b_{8} = b_{1} \cdot q^{7};\ \ \]
\[q^{7} = b_{8}\ :b_{1}\text{\ \ }\]
\[q^{7} = - 1000\ :0,0001\]
\[q^{7} = - \frac{10^{3}}{10^{- 4}}\text{\ \ }\]
\[q^{7} = - 10^{7}\text{\ \ }\]
\[Ответ:\ - 10.\]