We are given the following information.
t = 555 nm
n = 1.33
m = 3
We are asked to find the third longest wavelength that gives a minimum destructive interference at that point.
Recall that the destructive interference is given by

Re-arranging the above equation for wavelength.

Substitute the known values.

Therefore, the third longest wavelength that gives a minimum destructive interference at that point is 492.1 nm.