Two ships, A and B, set off from the upstream port A and the downstream port B of a river at the same time, and travel toward each other. The two ships meet at the midpoint of the river for the first time and continue to move forward. When A reaches port B and B arrives at port A , all return according to the original route. After the first encounter, they meet again after 4 hours. The known water velocity is 600 meters per hour. So how many meters is the distance between the boat A and the boat B at this time?
甲、乙两船分别从一条河的上游A港和下游B港同时出发，相向而行，两船在河道中点第一次相遇后继续前行，当甲到达B港，乙到达A港后，都按原路线返回，第一次相遇后，经过4小时它们又第二次相遇，已知水流速度每小时600米，那么此时甲船比乙船少行多少米？
<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">2_400 * 2</gadget>
<output>4_800</output>

<result>4_800</result>