\[\boxed{\mathbf{823\ (823).\ }Еуроки\ - \ ДЗ\ без\ мороки}\]
\[b_{7} = \frac{1}{2};\ \ q = 4\]
\[b_{7} = b_{6} \cdot q\ \ \]
\[b_{6} = \frac{b_{7}}{q} = \frac{1}{2 \cdot 4} = \frac{1}{8}\text{\ \ }\]
\[Ответ:b_{6} = \frac{1}{8}.\]