the mica sits on glass (n = 1. How thick should the sheet of mica (n = 1.

the mica sits on glass (n = 1.8). How thick should the sheet of mica (n = 1.5) be if it is to be as thin as possible and still give rise to destructive interference for reflection of light in the blue part of the spectrum (use l = 408 nm. How do I solve this???