I am attempting this past paper question and am not sure how to tackle this, this is not homework! :)

> 
> The spectrum of a distant quasar shows two broad emission lines with observed
>  wavelengths of 317.7nm and 404.7nm. The strongest lines are most likely to be either Lyman-α with a rest wavelength 121.6nm, CIV with a rest wavelength of 154.9nm or MgII with a rest wavelength of 280.0nm.
> 
> 
> (a) What is the redshift of the quasar? Please show your working.
> 
> 
> (b) What two lines have been detected?
> 
> 
> (c) The two lines have widths of 10nm and 20nm respectively. If I have measured
>  the mass of the black hole in the quasar to be 10^9Msun, how far from the centre of the quasar are the regions of ionised gas responsible for the emission lines?
>  Please specify any assumptions that you make to obtain your result.
> 
> 
> 

I am assuming I must find z to be the ratio of the change in wavelength to the rest wavelength. However I'm unsure of how to identify these in the question.