\[3x - 4 = b\]
\[3x = b + 4\]
\[x = \frac{b + 4}{3}\]
\[\frac{b + 4}{3} < 0\]
\[b + 4 < 0\]
\[b < - 4\]
\[Ответ:при\ \ b \in ( - \infty; - 4).\]