In a physics lab, light with a wavelength of 560nm travels in air from a laser to a photocell in a time of 17.3ns. When a slab of glass with a thickness of 0.870m is placed in the light beam, with the beam incident along the normal to the parallel faces of the slab, it takes the light a time of 21.1ns to travel from the laser to the photocell. What is the wavelength of the light in the glass? Use 3.00×10^8m/s for the speed of light in a vacuum. Express your answer using two significant figures.