Solving Thin Film Problem: Wavelength in Visible Spectrum

[wsuask]

A camera lens (n = 1.80) is coated with a thin film of magnesium fluoride (n = 1.45) of thickness 80.0 nm. What wavelength in the visible spectrum is most strongly transmitted through the film?

I have tried to solve this problem for quite a while now, and i hate to admit that there might be a small thing that i am missing. i have reached the following answers : 116 nm, 160 nm and 232 nm and all of them are wrong. I am using this formula: 2t= m*(lambda). I only have 2 tries left so please help me out. Also include a reason why you reached that answer. I have a final comming up and i would love to learn the propper way to do this. Thank you in advance.

 

[pam]

You want destructive interference for reflection at the first surface.
I think this means lambda in the glass=t.

 

[wsuask]

...

Thanks for your attempt, but I already figured out the correct way of doing it. The index of refraction of the MgF2 is the key to the answer.