1. The problem statement, all variables and given/known data I'm currently working through the following question: "A spaceship travels from Earth to the vicinity of the star that is measured by astronomers on Earth to be six light-years away. The spaceship and its occupants have a total rest mass of 32 000 kg. Assume that the spaceship travels at constant velocity. The time taken as measured by clocks on the spaceship is 2.5 years. Compute the velocity of the spaceship." 2. Relevant equations I have derived this equation which gives a velocity of 2.4 but I am confused about the units of this. 3. The attempt at a solution I thought automatically that the units would be light years per year but that doesn't make any sense? Or do the units cancel out somehow? Thank you!