An Optical Fiber Is Made of Clear Plastic with Index $\degree$

Multiple Choice

An optical fiber is made of clear plastic with index of refraction n = 1.50.For what angles with the surface will light remain within the plastic "guide"?

A) j < 66.6 $\degree$
B) j < 57.1 $\degree$
C) j < 51.7 $\degree$
D) j < 48.2 $\degree$