A Beam of Light in Air Is Incident on the Surface

Multiple Choice

A beam of light in air is incident on the surface of a rectangular block of clear plastic (n = 1.49) .If the velocity of the beam before it enters the plastic is 3.00 × 10⁸ m/s,what is its velocity inside the block?

A) 3.00E+8 m/s
B) 1.35E+8 m/s
C) 2.01E+8 m/s
D) 2.46E+8 m/s
E) 1.53E+8 m/s