Hello,
I have degrees in math, computational physics, chemistry, and a CS minor. I took an optics class in college and used Hecht's book. I also worked in an optics lab for a year. We studied quantum effect but used optics to study it.
Your problem:
Diamond has a wavelength of 243 nm, Zircon has a wavelength of 306 nm. you divide Diamond by Zircon to get .79. The formula to compute that is Wave= wave(Inital)/refractive index.
I can help you with this class, no problem. I look forward to speaking with you.