Two people start from A and B respectively at the same speed at the same time, and walk towards each other. The place where they meet for the first time is 7 kilometers away from A. After meeting, the two continue to move forward, return immediately after reaching the starting point of the other party, and meet for the second time at a distance of 5 kilometers from point B. What is the distance in kilometers between the two encounters?
两人以均匀的速度分别从A，B两地同时出发，相向而行，他们第一次相遇地点离A地7千米．相遇后两人继续前进，走到对方出发点后立即返回，在距B地5千米处第二次相遇，两次相遇之间的距离是多少千米．
<gadget id="calculator">21 - 7 - 5</gadget>
<output>9</output>

<result>9</result>