Bjorn is standing at x1 = 550 m. Firecracker 1 explodes at the origin and firecracker 2 explodes at x2 = 850 m. The flashes from both explosions reach Bjorn's eye at t = 4.0 \mu s.
At what time did Firecracker 1 explode?
At what time did Firecracker 2 explode?