Answer
Please see the work below.
Work Step by Step
We know that
$\lambda_{vacuum}=\frac{2nt}{m}$
We plug in the known values to obtain:
$\lambda_{vacuum}=\frac{2(1.33)(401\times 10^{-9}m)}{m}$
$\lambda_{vacuum}=\frac{1066.66nm}{m}$
for $ m=2$
$\lambda=\frac{1066.66nm}{2}=533.33nm $
We know that the wavelength of the green light ranges $520nm-565nm $.
Thus, $\lambda_{vacuum}=533.33nm $ shows that the absent reflected light is green light.
