\[(b + 1) \cdot x = 7\]
\[x = \frac{7}{b + 1}\]
\[\frac{7}{b + 1} < 0;\ \ \ \ 7 > 0\]
\[b + 1 < 0\]
\[b < - 1\]
\[Ответ:b < - 1.\]