Two beams of light start together and then hit a slab of two different kinds of material. This will cause one of the beams to get "ahead" of the other; that is, one will emerge from the slab sooner than the other. The beams have a wavelength of 570 nm outside the slabs, and the slab is d=2.3 μm thick. If the top half of the slab has index of refraction 1.79 and the bottom has index 1.39, by what time interval will one of the beams be ahead of the other once they've gone through the slab

Two beams of light start together and then hit a slab of two different kinds of material. This will cause one of the beams to get "ahead" of the other; that is, one will emerge from the slab sooner than the other. The beams have a wavelength of 570 nm outside the slabs, and the slab is d=2.3 μm thick. If the top half of the slab has index of refraction 1.79 and the bottom has index 1.39, by what time interval will one of the beams be ahead of the other once they've gone through the slab