Hi
A black car travelled from a to c at 60km per hour. A blue car took 4 hours to travel the same distance.  Both cars passed b at 2pm and the blue car reached c at 3pm. If b was 80km from c , what time did the black car leave a .

Thanks

He's WRONG!!!!

Blue car took 4 hours to get from a to c, got to c at @ 3:00 p.m., so it left "a" 4 hours before 3:00 p.m. or at 11:00 a.m.
Blue car passed b at 2:00 p.m., and got to c at 3:00 p.m., so it took 1 hour to get from b to c, which means that it took
3 hours to travel from a to b. As it's 80 km from b to c, and blue car took 1 hour for the trip, blue car's speed, from b
to c, was 80(1) = 80 km/h. That was also its speed from a to b.

Now, since blue car's speed was 80 km/h, and it took 3 hours to travel from a to b, then distance from a to b is 80(3) = 240 km.

With a speed of 60 km/h, the distance from a to b being 240 km, the black car's time taken to travel 240 km from a to b, would be  = 4 hours.

Since the black car took 4 hours to travel from a to b, it's obvious that the black car left "a" 4 hours before arriving at b, or 4 hours before 2:00 p.m. which was: 10:00 a.m.