it is the third question:
Here is my attempt at the question, i got up to the point where i need to find the angle of incidence from the prism to the air, but i dont know how to do that. The solution page says to use 60o minus the angle of refraction i just calculated, but i don't know why we need to do that.
if you could please tell me why we use that or how we get the angle from the prism to the air, that would be very helpful. thank you.