I'm doing a lab on helium and hydrogen emission spectra.

Question

so I got violet 20.35cm
blue/green 21.70cm
green 22.75
light green 23.08
yellow 27.70
red 31.70
faint red 33.95
and I also have the wavelenghts for helium spectra, its given. like for ex. violet is 380-420, my question is do I just pick a number in between 380-420?

my results for hydrogen lamp are
purple 19.57cm
green 22.47cm
yellow 26.95
red 31.00
the wavelenghts are not given in this exercise, once I figure out the y=mx+b equation from the helium spectra, do I then plug the data I got from hydrogen in the Y, and figure out X, which would give me the wavelength? Do you follow?