After jettisoning a stage, a rocket has a velocity of + 0.20c relative to the jettisoned stage.

Question:

After jettisoning a stage, a rocket has a velocity of + 0.20c relative to the jettisoned stage. An observer on Earth sees the jettisoned stage moving with a velocity of + 7.5 x 107 m/s, relative to her, in the same direction as the rocket. What is the velocity of the rocket relative to the Earth observer?