The drawing shows three materials, a, b, and c. A ray of light strikes the a–b interface at an angle that now barely exceeds its critical angle of 40.0°. The reflected beam then strikes the a–c interface at an angle of incidence that now barely exceeds its critical angle (which is not 40.0°). The index of refraction of material a is na = 1.88. Discover the indices of refraction for the two other materials.