An equilateral prism deviates a ray through 45° for two angles of incidence which differ by 20°. The angles of incidence are 
 

Angle of deviation d=i+e−A
45+60=i+e

When the emergent ray acts as incident ray,the devation is same.

$\begin{array}{r}e=i+20\\ 2i={85}^{\circ }\\ \Rightarrow i={42}^{\circ }{30}^{\mathrm{\prime }}\\ \Rightarrow e={62}^{\circ }{30}^{\mathrm{\prime }}\end{array}$