1. The problem statement, all variables and given/known data An electron moves to the right with a speed of 0.90c relative to the laboratory frame. A proton moves to the left with a speed of 0.70c relative to the electron. Find the speed of the proton relative to the laboratory frame. 2. Relevant equations Vx'=[Vx-V]/[1+(v2/c2)*Vx] 3. The attempt at a solution I have no idea where to start other than substituting 0.9c in for V.