Blue Light $\lambda$ _vac = 440 Nm )Shines onto a Plane of Glass

Blue light ( $\lambda$ _vac = 440 nm ) shines onto a plane of glass (n_glass = 1.50) .There is a thin layer of oil (n = 1.47) on top of this glass.What is the minimum thickness of the oil if there is constructive interference for the light?

A) 74.8 nm
B) 82.7 nm
C) 110 nm
D) 150 nm
E) 165 nm