Thin film red light green light interference

1. Homework Statement

A mixture of red light (wavelength vacuum = 652 nm) and green light (wavelength vacuum = 477 nm) shines perpendicularly on a soap film (n = 1.333) that has air on either side. What is the minimum nonzero thickness of the film, so that destructive interference removes the latter wavelength from the reflected light?

2. Homework Equations

HOW do I do this problem if this is a mixture of light? Do I simply add the wavelength value and if so at what point in the problem are they added??

3. The Attempt at a Solution
I used: sin(theta) = m (wavelength/n) and plugged in the value for n=1.333 and but I don't know what to plug in for wavelength.

Answers and Replies

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Doc Al
Mentor
Don't be adding any wavelengths, if that's what you're thinking. Read the problem more carefully:
What is the minimum nonzero thickness of the film, so that destructive interference removes the latter wavelength from the reflected light?
That's the wavelength you have to worry about.