1. The problem statement, all variables and given/known data Two events occur in an inertial system at the same time, but 9000 km apart. However in another inertial system these two events are observed to be 11000 km apart. What is the time difference between the two events in this second inertial system? 2. Relevant equations s^2=x^2+y^2+z^2-(ct)^2 3. The attempt at a solution since the spacetime interval is invariant in any inertial frame, s^2 can equal s'^2 for the first inertial system i got s^2=9m^2 putting it into the second equation i got 9m^2=11m^2-(ct)^2 subtracting 11m^2, dividing by -c, and taking the square root, i am left with 2.108*10^-8sec, which seems like it could be a reasonable answer, but it is not correct. can anyone tell me what i am doing wrong and lead me in the right direction please?