Answer:
4 hours.
Step-by-step explanation:
If the first guy is driving at 60 km, in 2 hours he is 120 km away. The second guy, leave two hours after. He will drive and in 2 hours he is 180 km. now if the second car keeps going then
120+ 60 + 60 +60 + 60 = 360
180 + 90 + 90 = 360.
So, the two hours for the guy going at 90 km and another 2 hours is 4 hours, so it will take 4 hours for the second driver to catch up.