For the problem below, I understand how to solve it using numbers, but I am having trouble understanding the physics/logic behind the solution. More specifically, I do not understand how the time of seeing the light flash is different compared to the actual arrival of light. Any assistance would be very helpful. Thanks. Experimenter A in reference frame S stands at the origin looking in the positive x-direction. Experimenter B stands at x = 900 m looking in the negative x-direction. A firecracker explodes somewhere between them. Experimenter B sees the light flash at t = 3.0 ms. Experimenter A sees the light flash at t = 4.0 ms. What are the spacetime coordinates of the explosion?