a patrol of timing paths each vehicle needs to travel the first half of the distance at a speed of 140 km / h. if the speed limit is 80km / h. which should be the highest average speed of the car in the second half of the section, to avoid being fined?
Drivers are ticketed and fined based upon instantaneous speed, not average speed. Slowing down in the second half of the trip should make no difference in the probability or amount of being ticketed and fined.
This is a nonsensical question in my opinion, and an indication of low quality math instruction from your school system or correspondence course.
Also, the expression "a patrol of timing paths each vehicle needs" makes no sense.