\[4x + 5 = 3b\]
\[4x = 3b - 5\]
\[x = \frac{3b - 5}{4};\ \ \ \ 4 > 0\]
\[3b - 5 > 0\]
\[3b > 5\ \ \]
\[b > 1\frac{2}{3}\]
\[Ответ:при\ b > 1\frac{2}{3}.\]