A light ray is travelling from a medium with an index of refraction of 1.39 and is incident at an interface with another medium at an angle of 48...

A light ray is travelling from a medium with an index of refraction of 1.39 and is incident at an interface with another medium at an angle of 48 degrees with the normal. The refracted angle is 23 degrees. What is the critical angle for total internal reflection if the light ray starts in the second medium first? Answer in degrees.