A Light Beam with Wavelength 500 Nm Is Reflected Constructively

Multiple Choice

A light beam with wavelength 500 nm is reflected constructively from a thin layer of oil having index of refraction 1.25. The oil floats on the top of water of index of refraction 1.33. What is the
Minimum thickness of the layer of oil?

A) 175 nm
B) 100 nm
C) 150 nm
D) 225 nm
E) 200 nm