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 redshift? (Note that the rest wavelength of the H $\alpha$ emission line is 656.3 nm.)

A) 0.05
B) 0.07
C) 0.10
D) 0.13
E) 0.15