An exterior angle of a triangle is $105^{\circ}$and its two interior opposite angles are equal. The equal angle is

Question

$\begin{array}{1 1} (a)\;37 \frac{1}{2}^{\circ} \\ (b)\;52 \frac{1}{2}^{\circ} \\ (c)\;72 \frac{1}{2} \\(d)\;75^{\circ} \end{array}$