$(20$ points$)$ A researcher measures the thickness of a layer of benzene $($ n$=1\mathrm{.}50)$ floating

on water $($ n$=1\mathrm{.}33)$ by shining monochromatic light onto the film and varying the

wavelength of the light. She finds that light of wavelength $575$ nm is reflected most

strongly from the film. What does she calculate for the minimum thickness of the film?

Draw a diagram showing the two paths the light takes.

PLEASE include the diagram!!