Consider plane wave light normally incident on a glass plate of stepped thickness (with a refractive index of 1.5) in air as shown in the figure below (dashed lines indicate wavefronts). Given the wavelength in air is 2 m and the thicknesses of the thin and thick glass sections are 0.5 m and 1.2 m, respectively, what is the distance between the wavefronts after the thin and thick glass sections, ? (1mark)