Step-by-step explanation:
are you sure you wrote the problem here correctly ?
because the distance will be 40km after less than half an hour just by the first car driving. way before the second car even starts.
to be precise, it would be after 60 minutes × 40 / 90
(= how many minutes of an hour are needed to reach 40km while going 90km/h) :
60 × 40 / 90 = 60 × 4 / 9 = 20 × 4 / 3 = 80/3 = 26.67 minutes.
but maybe the question was about 400km distance between the two cars.
so, the first car goes 90km/h for 2 hours.
at that moment it will be 2×90=180km ahead.
that would mean that 220km are still missing for the 400km assumption.
with each hour driving the first car makes 20km more than the second car.
to build up 220km that way would require
220/20 = 11 hours.
plus the 2 original head start hours this would make 13 hours as overall answer.
