First. Two people, B, set off from A and B at the same speed at the same time, and walk towards each other. The place where they first meet is 8 kilometers away from A. After meeting, the two continue to move forward, go to the starting point of the other party and return immediately, and meet for the second time at a place 4 kilometers away from B, so how many kilometers is the distance between A and B?
甲．乙两人以均匀速度分别从A、B两地分别同时出发，相向而行，他们第一次相遇地点距离A地8千米．相遇后两人继续前进，走到对方出发点立即返回，在距B地4千米的地方第二次相遇，那么AB两地的距离为多少千米？
<gadget id="calculator">8 * 3</gadget>
<output>24</output>

<gadget id="calculator">24 - 4</gadget>
<output>20</output>

<result>20</result>