A covered 240km at 60km/h and 80km at 100km/h and 200km at 50km/h.what is the average speed during the whole journey

Average speed = total distance traveled divided by total elapsed time. So you first neeed to determine (a) what is the total distance traveled, and (b) what's the total time? The time for each segment is the distance traveled for that segment divided by the speed for that segment.