Optics

Refraction is the change of direction that occurs then a light ray passes through a transparent object. Normal is the line perpendicular from the entry point of the light 

* always bends towards the normal from air to glass 

* bends away from the normal from glass to air

* bends toward the normal when passing into a more reactive substance and opposite for when it pass into a less reactive

the refractive index is the speed of light in free space/ speed of light in the substance.

* refractive index = n, angle of incidence = i, and of refraction = r

n = sin i / sin r 

so i = 40' and n= 1.5 

rearrange: sin i / n = sin40 / 1.5 = 0.429 

shift sin-1 therefore r = 25'