The improved Hubble constant value is 73.2 kilometers per second per megaparsec. (sciencedaily.com)
Astronomers on galaxy (a) will see the galaxy (c) moving away at (770 + 770) kilometers / second = 1,540 kilometers / second, twice as fast as galaxy (b), because galaxy (c) is at a distance of (10 + 10) megaparsecs from galaxy (a), twice as far as galaxy (b). (astronomynotes.com)
The distances between galaxies are large and are often measured in megaparsecs. (astronomynotes.com)