Cars A and B set off from places A and B at the same time and drive towards each other. They meet for the first time at a distance of 40 kilometers from point A, return immediately after arriving at the destination, and meet for the second time at a distance of 20 kilometers from point B. What is the distance between places A and B? In this way, where will the two cars meet for the third time?
甲、乙两车分别同时从A、B两地出发，相向而行，在距A地40千米处第一次相遇，到达目的地后立即返回，在距B地20千米处第二次相遇，A、B两地距离多少？照这样走法，两辆车第三次相遇在什么地方．
<gadget id="calculator">40 * 3</gadget>
<output>120</output>

<gadget id="calculator">120 - 20</gadget>
<output>100</output>

<result>100</result>