Answer:
572.3 nm
Step-by-step explanation:
= refractive index of the oil film = 1.48
= thickness of the oil film = 290 nm
= wavelength of the dominant color
m = order
Using the equation

For m = 0

= 1716.8 nm
For m = 1

= 572.3 nm
For m = 2

= 343.4 nm
Hence the dominant color wavelength is 572.3 nm