Final answer:
According to Hubble's law, if Galaxy B is three times farther away from us than Galaxy A, Galaxy B will be moving away at a speed three times greater than Galaxy A.
Step-by-step explanation:
According to Hubble's law, the velocity at which a galaxy is receding from us is directly proportional to its distance from us. If Galaxy B is three times farther away from us than Galaxy A and both galaxies are not part of our Local Group, then according to Hubble's Law, Galaxy B will be moving away from us at a speed that is three times greater than the speed at which Galaxy A is receding.
This is because Hubble's Law states that velocity (v) = Hubble constant (H0) × distance (d), so if Galaxy B's distance is three times the distance of Galaxy A, its velocity, according to this relation, will also be three times greater, assuming H0 is constant over this distance. Moreover, Hubble's observation reveals that the universe is expanding, and this expansion is typically uniform, meaning that the farther away a galaxy is, the faster it is moving away from us.