posted by slien .
Imagine a motorcycle rider moving with a speed 0.7c past a stationary observer. If the rider tosses a ball in the forward direction with a speed of 0.6c, relative to himself, what is the speed of the ball as seen by the stationary observer? Ans in units of c.
The addition of velocities formula says
You can do it all in units of c, so plug in u=0.7 and v=0.6 to get approximately 0.92.