In a Newton's rings experiment in laboratory source of light having two wavelengths 6000Å and 4500Å is used. It is found that nth dark ring due to 6000Å coincides with (n+1)th dark ring due to 4500Å. Evaluate the radii of nth dark rings due to 6000Å and 4500Å if radius of curvature of the palno-convex lens is 100cm.