If You Found a Galaxy with an H $\alpha$ Emission Line That Had a Wavelength of 756

Multiple Choice

If you found a galaxy with an H $\alpha$ emission line that had a wavelength of 756.3 nm, what would be the galaxy's distance if the Hubble constant is 70 km/s/Mpc? (Note that the rest wavelength of the H $\alpha$ emission line is 656.3 nm.)

A) 650 Mpc
B) 760 Mpc
C) 3,200 Mpc
D) 6,400 Mpc
E) 7,600 Mpc