Using the geometry we can find refraction angle Θ.
Using Snell’s law we can find index of refraction of the medium
By assuming index of refraction on air is one (n1 = 1).
n2 = 1.9917
Index of refraction of the medium is 1.9917
Using above result we can find speed of light ray inside the medium
C = speed of light (Approximately 3 x 108 m/s)
Speed of light ray inside the medium is 1.506 x 108 m/s
Using geometry we can find distance AB
Distance from point A to B is 6.5 meters.
Using the distance and velocity inside the medium we can find the time taken to light ray to travel from point A to B.
Velocity = Distance / Time
Time = Distance / Velocity
Time = 6.5 m / 1.506 x 108 m/s
Time = 4.316 x 10-8 s
Time to light ray to travel from point A to B is 4.316 x 10-8 seconds.