A ray of light travelling in the direction  $\frac{1}{2}(\widehat{i}+\sqrt{3}\widehat{j})$  is incident on a plane mirror. After reflection, it travels along the direction $\frac{1}{2}(\widehat{i}-\sqrt{3}\widehat{j})$  . Then angle of incidence is $6\theta$ (in degree). Find the value of $\theta$.