Physics Help Plz?

[canadianhifive]

A soap film (n = 1.34) is contained within a rectangular wire frame. The frame is held vertically so that the film drains downward and becomes thicker at the bottom than at the top, where the thickness is essentially zero. The film is viewed in white light with near-normal incidence, and the first violet (lambda = 416 nm) interference band is observed 2.88 cm from the top edge of the film. Locate the first red (lambda = 677 nm) interference band.

Determine the film thickness at the position of the violet band