An experimenter arranges to trigger two flashbulbs simultaneously, producing a big flash located at the origin of his reference frame and a small...

An experimenter arranges to trigger two flashbulbs

simultaneously, producing a big flash located at the origin of his

reference frame and a small flash at x = 30.0 km. An observer

moving at a speed of 0.250c in the positive direction of x also views

the flashes. (a) What is the time interval between them according

to her? (b) Which flash does she say occurs first?