Two optically flat glass plates, L = 16 cm long, are in contact at one end and separated by d = 0.020 mm at the other end. The space between the plates is occupied by oil with index of refraction n1 = 1.45. The index of the glass plates is n2 = 1.55. The plates are illuminated at normal incidence with monochromatic light, and fringes are observed. The monochromatic light has a wavelength in vacuum of ? = 580 nm. What is the number m of bright fringes which are visible?