Answer:
Step-by-step explanation:
We need to find the index of refraction n₂ for the prism.
I will ASSUME the prism sits in air where n₁ = 1.00
With total internal reflection (Snell's law)
n₂sin42 = 1.00sin90
n₂ = 1/sin42 = 1.494476... = 1.49
now we can look at the ray entering the prism.
The ray strikes surface 2 at an angle of 90 - 42 = 48°
Meaning it leaves surface 1 at an angle of 180 - 48 - 60 = 72°
so the angle of incidence at surface 1 is 90 - 72 = 18°
1.00sinθ₁ = 1.49sin18
θ₁ = 27.5°