you would divide 180 and 3, that's how much car a travels in an hour. Do the same for car b so 100÷2
you would get 60 for 'a' and 50 for 'b'
but you still need to find how much in four hours so you would times those numbers by 4
car a- 240 in 4 hours
car b- 200 in 4 hours
so they would be 40 apart
hope that made sense :)