Light of wavelength 600 nm in vacuum is incident nearly perpendicularly on a thin film whose index of refraction is 1.5. the light travels from the top surface of the film to the bottom surface, reflects from the bottom surface, and returns to the top surface, as the drawing indicates. what is the total (down-and-back) distance traveled by the light inside the film? express your answer in terms of the wavelength λfilm of the light within the film.