An experimenter arranges to trigger two flashbulbs simultaneously, a blue flush located at the origin of his reference frame and a red flush at x $=30\mathrm{.}4$ km$.$ A second observer, moving at speed $0\mathrm{.}247$c in the direction ofincreasing x$,$ also views the flushes.$($a$)$ What time interval between them does she find?$($b$)$ Which flush does she say occurs first?