2 planes started at the same time from two airports that are 3600 km. One flew 792 mad other flew 888 . In how many hours were the plane still 240 km apart?

Question

For this problem, I dont really understand how you can find the answer. 

Answer 1

the two airports are 3600 km apart and the planes fly towards each other until they are 240 km apart from each other

the planes are flying at a rate of 792km/hr and 888km/hr

3600-240=3360

792x+888x=3360 where x=# of hours the planes fly towards each other and travel a total distance of 3360 km which will leave them 240 km apart

solve the equation

1680x=3360

x=3360/1680

x=2 hours