\[\boxed{\mathbf{801}\mathbf{.}}\]
\[y = \sqrt{3x - 7} = (3x - 7)^{\frac{1}{2}}\]
\[y^{'} = \frac{1}{2} \bullet 3 \bullet (3x - 7)^{\frac{1}{2} - 1} =\]
\[= \frac{3}{2} \bullet (3x - 7)^{- \frac{1}{2}} = \frac{3}{2\sqrt{3x - 7}}\]
\[\sqrt{3x - 7} = \frac{3}{2\sqrt{3x - 7}}\]
\[3x - 7 = \frac{3}{2}\]
\[3x = \frac{3}{2} + 7 = \frac{3}{2} + \frac{14}{2} = \frac{17}{2}\]
\[x = \frac{1}{3} \bullet \frac{17}{2} = \frac{17}{6} = 2\frac{5}{6}.\]
\[Ответ:\ \ 2\frac{5}{6}.\]