The topic is easy to understand wrong. The speed of two people is different, and they arrive at different places after a few hours, that is, two people accelerate their return from different places. There should be two places where you can turn, and the speed of two people is different. The last question is not clear. But there is "a few hours in advance" in the title, which means that the turning point time from A to A is the same as the turning point time from B to B. The title question should be "How many hours are the agreed hours in advance?"

Set it to x hours, 7X/(7+3)-6X/(6+3)=6/60 x=3 hours.