Refer to the following information for the next twelve questions.
A thin layer of baby oil (n = 1.50) is floating on the top of the water (1.33) in a wadding pool.
We will now use the formula EPD = 2t + Φ to calculate the thickness of the oil film for a given wavelength of light. In this formula,

EPD represents the extreme path difference traveled by rays 2 and rays 3, 4, and 5 collectively before reaching the eye.

2t represents twice the thickness of the film since rays 3 and 4 have to travel down and back up through the film.
This thickness will be represented in terms of the number of wavelengths the light rays travel in the film, λ_{n}, where λ_{n} = λ/n

Φ represents the net phase inversion (or phase difference) between rays 2 and 5. It will always be equal to either 0 λ_{n} or ½ λ_{n}.
Remember that all wavelengths must be expressed in terms of what happens in the film: we always use 0 λ_{n} or ½ λ_{n}
Which of the following expressions should be used to mathematically represent the cancellation of these rays resulting from rays 3 and 4 traveling through this thin film of oil? 
 

Which formula correctly summarizes our current information: 



