1. The problem statement, all variables and given/known data An observer in frame S standing at the origin observes two flashes of coloredlight separated spatially by delta x=2400 m. A blue flash occurs first, followed by a red flash 5 microseconds later. An observer in S' moving along x axis at speed v relative to S also observes the flashes 5 microseconds apart and with a separation of 2400m, but the red flash is observed first. Find the magnitude and direction of v. This is the only prob. on the hw that i seem to have no clue where to start. 3. The attempt at a solution I know that the fact that the blue and red light switch places in terms of appearance (1st, 2nd) is the key factor in figuring out how to solve this problem, but i don't really know what this is telling me(i.e. what information it is providing me with). Any help/hint would be greately appreciated.