A ray of light passes through an equilateral prism such that the angle of incidence is equal to the angle of emergence and each one is equal to $\large\frac{3}{4}$ th the angle of prism. Then angle of deviation is :

Question

\[\begin {array} {1 1} (1)\;45^{\circ} & \quad (2)\;39^{\circ} \\ (3)\;20^{\circ} & \quad (4)\;30^{\circ} \end {array}\]