A thin film of oil (n = 1.26) is located on a smooth, wet pavement. When viewed perpendicular to the pavement, the film appears to be predominantly red (640 nm) and has no component of wavelength 512 nm. How thick is the oil film? I'm getting confused by the use of two wavelengths in this problem... I'm pretty sure I need to use the equation 2nt = (m+1/2)lambda and solve for t. But what wavelength do I use? I don't understand what it means when it says "...has no component of wavelength 512nm" Can someone help me with this?