At a science museum, Marlow looks down into a display case and sees two pieces of very flat glass lying on top of each other with light and dark regions on the glass. The exhibit states that monochromatic light with a wavelength of 550 nm is incident on the glass plates and that the plates are sitting in air. The glass has an index of refraction of 1.51. 

(a) What is the minimum distance between the two glass plates for one of the dark regions? 

(b) What is the minimum distance between the two glass plates for one of the light regions? 

(c) What is the next largest distance between the plates for a dark region?