A and B start from both places A and B at the same time. Walking towards each other, everyone keeps moving back and forth between AB and AB. For the first time, they meet at C, which is 3 kilometers away from A, and when they return, they meet for the second time at D, 2 kilometers away from B. Find The distance between AB and AB.
甲乙两人从A、B两地同时出发．相向而行，每人都在AB两地间不停地来回运动，第一次在距离A地3千米的C处相遇，各自返回时在距离B地2km的D处第二次相遇，求AB两地间的距离．
<gadget id="calculator">3 * 3</gadget>
<output>9</output>

<gadget id="calculator">9 - 2</gadget>
<output>7</output>

<result>7</result>