\[(b - 3)x = b² - 9\]
\[x = \frac{(b - 3)(b + 3)}{b - 3};\ \ b \neq 3\]
\[x = b + 3\]
\[b + 3 > 0\]
\[b > - 3\]
\[Ответ:( - 3;3) \cup (3;\ + \infty).\]