In a $\Delta ABC, \frac{a}{b}$$=2+\sqrt 3$ and $\angle C=60^{\circ}$. Then the ordered pair $\angle A, \angle B) $ is equal to :

Question

$\begin{array}{1 1} (15^{\circ},105^{\circ}) \\ (105^{\circ},15^{\circ}) \\ (45^{\circ},75^{\circ}) \\ (75^{\circ},45^{\circ}) \end{array} $