A thin layer of oil $($n$=1\mathrm{.}252$n$=1\mathrm{.}252)$ is floating on water. What is the minimum thickness of the oil in the region that strongly reflects light with a wavelength of $569$nm $($in air$).$ Use n$=1\mathrm{.}333$n$=1\mathrm{.}333$ for the index of refraction of water. Hint: Be careful when using the thin film interference equations because sometimes there is a $180$ phase shift on reflection, and sometimes there is not.