Ray Optics and Optical Instruments Part 1

In figure, the optical fiber is l=2 m long and has a diameter of d=20µm. If a ray of light is incident on one end of the fiber at angle θ1=40°, the number of reflections it makes before emerging from the other end is close to : (refractive index of fiber is 1.31 and sin‌40°=0.64)