1. The problem statement, all variables and given/known data Suppose on a spacetime diagram, an event happens at x=-4, t=5 and another event happens at x=0 and t=6. If there is a frame such that the two events happen simultaneously, what would the relative speed of that frame be? 2. Relevant equations 3. The attempt at a solution I know this interval is spacelike ( between the two events) but the answer says Relative speed=Beta=Delta(t)/Delta(x)=0.25 But I do not understand why is the speed=time over distance here?