The conventional approach to this question would be to find the velocity in metres per second, and then convert it to kilometres per hour.
But the easiest approach is more simple:
Distance = 600m = 0.6km
Time = 5min = (5/60)hrs = (1/12)hrs
Speed = Distance/Time = (0.6)/(1/12) = 12(0.6) = 7.2kmph