Interference and the wave nature of light?

A soap film with different thicknesses at different places has an unknown refractive index n and air on both sides. In reflected light it looks multicolored. One region looks yellow because destructive interference has removed blue (vacuum = 482 nm) from the reflected light, while another looks magenta because destructive interference has removed green (vacuum = 539 nm). In these regions the film has the minimum nonzero thickness t required for the destructive interference to occur. Find the ratio tmagenta/tyellow.