I need help for a assignment NOT A QUIZ

Sound is a disturbance that travels through a medium as a

What is the thinnest soap film (excluding the case of zero thickness) that appears black when illuminated with light with a wavelength of 480 ? the index of refraction of the film is 1.34, and there is air on both sides of the film. express your answer in nanometers. hint 1. how to approach th

This is the number of complete movements of a wave per second.