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 = 1.64) .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) 3.00 × 10⁸ m/s
B) 1.12 × 10⁸ m/s
C) 1.83 × 10⁸ m/s
D) 2.34 × 10⁸ m/s
E) ​1.08 × 10⁸ m/s