\[(b + 4)x = b² - 16\]
\[x = \frac{(b - 4)(b + 4)}{b + 4};\ \ \ \ \ b \neq - 4\]
\[x = b - 4\]
\[b - 4 < 0\]
\[b < 4\]
\[Ответ:( - \infty;\ - 4) \cup ( - 4;4).\]