Solving a problem in physics section 1 point 72 optics

72. On a plane-parallel glass plate 1 cm thick beam of light falls at an angle of 60°. The refractive index of glass 1.73. Part of the light is reflected and part is refracted, held in the glass, it is reflected from the bottom surface of the plate and refracted again, back into the air parallel to the first reflected beam. L Determine the distance between the beams.