A film of oil that has an index of refraction of 145 rests

Question

Question: A film of oil that has an index of refraction of 1.45 rests on an optically flat piece of glass of index of refraction n = 1.60. When illuminated with white light at normal incidence, light of wavelengths 684 nm and 456 nm is predominant in the reflected light.

Part A: Determine the thickness of the oil film.

..... nm

Please show all work and steps to find the thickness of the oil film.