We know the propagation speed is 100km/hr, travelling distance is 150 km and each tollbooth services a car at a rate of one car per 12 seconds. In additional, there are 10 cares. The time taken by a car to travel 150km is 150km/100km/hr = 1.5 hr = 90 min The overall tollbooths service time for 10 cars is 12*3*10 = 360 seconds = 6 min Finally, the end to end time delay for 10 cars is 90 min + 6 min = 96 min b. For 8 cars, the overall tollbooths service time should be 12*3*8= 288 seconds = 4.8 min Finally, the end to end time delay for 8 cars is 90 min + 4.8 min = 94.8 min