A thin film (n = 1.25) is deposited on a glass plate (n = 1.40) and illuminated

Question:

A thin film (n = 1.25) is deposited on a glass plate (n = 1.40) and illuminated with light of wavelength 550nm (measured in air). The light beam is perpendicular to the plate.
What is the minimum (nonzero) thickness for the film that will
(a) Maximally transmit and
(b) Maximally reflect the light?