To determine the distance to this quasar using the Hubble relation (assuming the redshift is cosmological in origin) we do the following steps:

1.  Measure the redshift off the spectrum above:  3C 273 Hydrogen beta line redshift Dl = l - lo = 77.9 nm

2.  Use the doppler relation to determine the radial velocity:  v/c = Dl/lo   (lo = 486.1 nm, Hb rest wavelength)  v = (77.9 nm / 486.1 nm) x 300,000 km/s = 48,000 km/s

3.  Use the Hubble relation with the current best value of Hubble's constant (Ho = 71 km/s/Mpc) to determine the distance:   D = v/Ho ;       D = 48,000 km/s / 71 km/s/Mpc ;     D = 677 Mpc = 2.2 billion light years