Answer
$u=\frac{\pi}{6}+n\pi$
Work Step by Step
$3\sqrt 3~tan~u=3$
$tan~u=\frac{3}{3\sqrt 3}=\frac{\sqrt 3~·\sqrt 3}{3\sqrt 3}$
$tan~u=\frac{\sqrt 3}{3}$
The period of $tan~u$ is $\pi$. The solution in the interval: $[0,\pi)$ is:
$u=\frac{\pi}{6}$
Now, add multiples of $\pi$ to the solution:
$u=\frac{\pi}{6}+n\pi$
