Calculations with wavelength and frequency
Key Questions

If you note the units you are using, it becomes easier.
You have
#1/"s"# , and oftentimes with wavelength, you want to convert to#"nm"# which is UVVis range (#"200~700 nm"# ), and is often of spectral interest.What you want to do is:
#1/"s" > 1/"m" > "m" > "nm"# Conversion factors are extremely useful, and one easy one to remember is the speed of light, which is about
#"3" xx 10^8 "m/s"# .#1/(1/cancel("s") * cancel("s")/"m") = "m"# And finally, we can convert to
#"nm"# :#10^9 "nm" = "1 m" > "conversion factor: "(10^9 "nm")/("1 m")# #cancel"m" * (10^9 "nm")/(1 cancel"m")# Thus, overall, you just have:
#color(blue)("nm") = 1/(1/cancel("s") * cancel("s")/(3xx10^8 cancel"m")) * (10^9 "nm")/(1 cancel"m")# #= color(blue)(1/(1"/"cancel("s"))*3xx10^8 cancel("m")"/"cancel("s") xx (10^9 "nm")/(1 cancel"m"))#