Sagot :
Answer:
Assuming the last lap took the time T, then the other laps took times of 6T, 3T respectively 2T. Total time: 12T, including the last lap.
Now let's calculate the distances. The last lap took the distance of, say, d. 60 km/h in time T means the distance d=60T.
OK, the total distance is 4d=240T, while the total time is 12T. Divide, you get 20 (km/h)