The walls of a soap bubble have about the same index of refraction as that of plain

Question:

The walls of a soap bubble have about the same index of refraction as that of plain water, n = 133. There is air both inside and outside the bubble.
(a) What wavelength (in air) of visible light is most strongly reflected from a point on a soap bubble where its wall is 290nm thick? To what color does this correspond?
(b) Repeat part (a) fur a wall thickness of 340nm.