1. The problem statement, all variables and given/known data Two spaceships (A and B) are travelling in opposite ways. An observer in Earth measures both velocities. The speed of ship A (Va) = 0.75c. The speed of ship B (Vb) = 0.85c. What's the speed of **** B regarding ship A? 2. Relevant equations 3. The attempt at a solution At first I tried solving it using Galileu's relativity, but I've reached the result of 1.6c. Then I remembered that when we're dealing with speeds close to c we have to use Einstein's special relativity, so I've looked around all the formulas I have but none of them involved velocity, only time, spaceship length, and there are also the ones involving energy but I don't think that has nothing to do with this exercise. Thanks!