Hi - I'm having trouble with the following problem: A mixture of yellow light (wavelength = 574 nm in vacuum) and violet light (wavelength = 418 nm in vacuum) falls perpendicularly on a film of gasoline that is floating on a puddle of water. For both wavelengths, the refractive index of gasoline is n = 1.40 and that of water is n = 1.33. What is the minimum nonzero thickness of the film in a spot that looks the following colors because of destructive interference, for yellow light? Because its destructive interference, I'm using the equation t = lambda/2 ,but this is leading to the wrong answer. I'm also making the wavelength for the yellow light equal 410 (574/1.40). Where am I going wrong, or am I even using the right equation? Thanks for your help!