A 500-Nm-Wavelength Beam of Light Illuminates a Soap Film with Air

A 500-nm-wavelength beam of light illuminates a soap film with air on both sides and an index of refraction 1.33. If the beam of light is incident normally on the film, what is the minimum thickness
Of the film to make the reflected light enhanced in brightness?

A) 94.0 nm
B) 74.0 nm
C) 268 nm
D) 152 nm
E) 47.0 nm