(b)
$\because\tan{\left( x + \frac{\pi}{3} \right) \geq 1 \Rightarrow \frac{\pi}{4} \leq x + \frac{\pi}{3} < \frac{\pi}{2}}$
$\Rightarrow - \frac{\pi}{12} \leq x < \frac{\pi}{6}$
$\Rightarrow n\pi - \frac{\pi}{12} \leq x \leq n\pi + \frac{\pi}{6}$