The average speed of a car is the ratio of total distance travelled to the time taken to travel all that distance. In this case, the car traveled 45 km in the first hour and then it traveled 78 km in each of the next two hours. Thus, the total distance traveled is:
D = 45 + 78 + 78 = 201 km.
The time taken to travel this distance is 1 + 2 = 3 hours.
Thus, the average speed of the car is 201/3 = 67 km/hr.
We can also convert the average speed in meter per second, using the knowledge that a km has 1000 meters and one hour has 3600 seconds.
Thus, average speed = 67 km/hr = 67 x 1000/3600 m/s = 18.6 m/s.
Hope this helps.