A machine gun is mounted on an armored car moving with a speed of `20 ms^(-1)`. The gun point against the direction of motion of car. The muzzle speed of bullet is equal to speed of sound in air i.e., `340 ms^(-1)`. The time difference between bullet actually reaching and sound of firing reaching at a target `544 m` away from car at the instant of firing is reaching at a target `544 m` away from car at the instant of firing is