\[\sqrt{x - 3} = 19 - 5x\]
\[t = \sqrt{x - 3}\]
\[5t^{2} + t - 4 = 0\]
\[t_{1} = - 1;\ \ \ t_{2} = \frac{4}{5}\]
\[1)\ \sqrt{x - 3} = - 1;\ \ \ \ \]
\[\sqrt{x - 3} \geq 0 \Longrightarrow нет\ решения.\]
\[2)\ \sqrt{x - 3} = \frac{4}{5}\ \]
\[x - 3 = \frac{16}{25}\]
\[x = 3\frac{16}{25}\]
\[Ответ:3\frac{16}{25}\text{.\ }\]