Two cars start at the same time between stations A and B, drive towards each other, and drive back and forth. The first encounter is at a distance of 40 kilometers from station A, and the second encounter is at a distance of 20 kilometers from station B. Ask A and B How far apart are the stations?
两辆汽车在甲、乙两站之间同时出发，相向而行，往返行驶，第一次相遇在距甲站40公里处，第二次相遇在距乙站20公里处，问甲、乙两站相距多远？
<gadget id="calculator">3 * 40</gadget>
<output>120</output>

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

<result>100</result>