When a light ray travels from one medium to another, its direction changes, because the velocity of light changes according to the medium.
The refractive index is the degree of the change of the direction of the light in two mediums.
The refractive index n=c∕v
From the question, it is given that the speed of the light in the air is c=3×108m∕ s
the refractive index of the medium A is nA=1.5 that of medium B is nB=1.33
the velocity of light in medium A is v=c∕nA =3×108∕1.5=2×108m∕ s
the velocity of light in medium B is v=c∕nB =3×108∕1.33=2.2×108m∕ s