What is the minimum thickness of an oil layer floating on water which appears red $700nm)$ when white light illuminates the layer? Consider that the incident light is parallel with the normal to the oil surface, $n_{\text{o}\text{i}\text{l}}=1\mathrm{.}48,$ and $n_{\text{w}\text{a}\text{t}\text{e}\text{r}}=1\mathrm{.}30.$

Select one:

a$.238nm$

b$.274nm$

c$.126nm$

d$.118nm$