Person A and Party B respectively set off from two places AB at the same time, and the first meeting is 6 kilometers away from point A. After meeting, A and B continue to move forward and return when they reach AB. The second encounter is 3 kilometers away from point B. Find the distance between A and B.
甲乙二人分别从AB两地同时相向出发，第一次相遇距离A点6公里．相遇后，甲乙二人继续前行并且在到达AB两地返回，第二次相遇距离B点3公里．求AB两地之间的距离．
<gadget id="calculator">6 * 3</gadget>
<output>18</output>

<gadget id="calculator">18 - 3</gadget>
<output>15</output>

<result>15</result>