A Uniform Film of Oil (N = 1 $\lambda$ = 450 Nm and a Brightness Minimum At

Short Answer

A uniform film of oil (n = 1.31)is floating on water.When sunlight in air is incident normally on the film,an observer finds that the reflected light has a brightness maximum at $\lambda$ = 450 nm and a brightness minimum at $\lambda$ = 600 nm.What is the thickness of the oil film?