If the Spectrum of a Distant Galaxy Is Observed to Have

Multiple Choice

If the spectrum of a distant galaxy is observed to have a calcium K absorption line that occurs at a wavelength of 500.4 nm, what is this galaxy's distance if the rest wavelength of this absorption line is 393.4 nm? Assume the Hubble constant is 70 km/s/Mpc.

A) 720 Mpc
B) 950 Mpc
C) 1,200 Mpc
D) 2,500 Mpc
E) 3,700 Mpc