\[\sqrt{x - 4} = 19 - 4x;\ \ \ \ \ \ t = \sqrt{x - 4}\]
\[4t^{2} + t - 3 = 0\]
\[t_{1} = - 1;\ \ \ t_{2} = \frac{3}{4}\]
\[1)\ \sqrt{x - 4} = - 1;\ \ \ \]
\[\sqrt{x - 4} \geq 0 \Longrightarrow нет\ решения.\]
\[2)\ \sqrt{x - 4} = \frac{3}{4}\]
\[x - 4 = \frac{9}{16}\]
\[x = 4\frac{9}{16}\]
\[Ответ:\ 4\frac{9}{16}.\]