We wish to coat a flat slab of glass (n = 1.50) with a transparent material (n = 1.25) and illuminate with light of wavelength 600 nm (in vacuum). For what minimum thickness of the coating will the light be (a) reflected back to the observer and (b) transmitted during the glass (i.e. no reflection back to the observer)? [Note: t = 0 is not an answer for (b)].