The Giant-Impact Hypothesis suggests that 4.5 billion years ago a Mars sized proto- planet named Theia collided with the earth ejecting enough matter into space to coalesce and form the moon. Theia was traveling 4.2 km/s and was 0.45 the mass of the earth when it collided. Assuming earth to be the inertial frame of reference, what was the resulting linear velocity of the Earth-Moon system after the collision?