Answer:

Step-by-step explanation:
The index of refraction
is a number that describes how fast light propagates through a medium or material.
Being its equation as follows:
(1)
Where
is the speed of light in vacuum and
its speed in the other medium.
So, from (1) we can find the velocity at which the light travels and then the time it requires to travel :
(2)
For medium 1:

(3)
(4)
For medium 2:

(5)
(6)
On the other hand, the velocity
is the distance
traveled in a time
:
(7)
We can isolate
from (7) and find the value of the required time:
(8)
In this case the total time will be:
(9)
Where:
is the distance the light travels in medium 1
is the distance the light travels in medium 2
is the velocity of light in medium 1
is the velocity of light in medium 2
(10)
Finally:
(10)