A prism of angle 75^° and refractive index √ 3 is coated with thin film of refractive index 1.5 only at the back exit surface. To have total internal…

A prism of angle $\displaystyle 75^{\circ}$ and refractive index $\displaystyle \sqrt{3}$ is coated with thin film of refractive index $\displaystyle 1.5$ only at the back exit surface. To have total internal reflection at the back exit surface the incident angle must be $\displaystyle \_\_\_\_$. $\displaystyle \left(\sin 15^{\circ}=0.25\right.$ and $\displaystyle \left.\sin 25^{\circ}=0.43\right)$