Answer:
176.22 nm
Explanation:
[tex]n[/tex] = Index of refraction of oil = 1.64
[tex]\lambda[/tex] = Wavelength of the light = 578 nm
[tex]t[/tex] = minimum thickness of the oil
For destructive interference, we have
[tex]2nt = m \lambda[/tex]
For minimum thickness, m = 1
[tex]2(1.64)t = (1) (578)\\3.28 t = 578\\t = 176.22 nm[/tex]