\[3x - 2\sqrt{x} - 8 = 0\]
\[Пусть\ \ t = \sqrt{x}:\]
\[3t^{2} - 2t - 8 = 0\]
\[D = 4 + 96 = 100\]
\[t_{1,2} = \frac{2 \pm 10}{6} = 2;\ - \frac{4}{3}\]
\[\sqrt{x} = 2\ \ \ \ \ \ \ \ \ \ \ \sqrt{x} = - \frac{4}{3}\]
\[x = 4\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \varnothing\]
\[Ответ:\ 4.\]