A perfectly flat thin piece of glass (n=1.5) that is 6cm long and 2cm wide is placed over a perfectly flat piece of black plastic (n=1.2) that is the same size. One end of the glass is slightly elevated while the other end is in contact with the plastic. Light of wavelength 600nm is incident normally from above. One observes dark fringes at locations of 0cm, 1cm, 2cm, 3cm, 4cm, 5cm, and 6cm from the end that is in contact by the plastic. How thick is the air gap among the glass and plastic at the elevated end of the glass?