Consider the optical fiber shown in the drawing below. The innermost layer (the core) is made of OptoFlex, with an index of refraction 2.48. The cladding surrounding the core is made of plexiglass with index of refraction 1.39. 

Find the critical angle of incidence, LaTeX: theta_cθ c, in degrees, such that light travelling in the core at angles larger than LaTeX: theta_cθ c will remain in the core?