Red Light Is Viewed Through a Thin Vertical Soap Film $\lambda$

Multiple Choice

Red light is viewed through a thin vertical soap film.At the third dark area shown, the thickness of the film, in terms of the wavelength $\lambda$ within the film, is:

A) " $\lambda$ /4"
B) " $\lambda$ /2"
C) " $\lambda$ "
D) "3 $\lambda$ /4"
E) "5 $\lambda$ /4"