Car A starts from point A, and car B from point B travels towards each other at the same time. After arriving at point A, car B returns immediately without stopping, and catches up with car A at a distance of 140 kilometers from point B. It is known that the speed of car A is 20 km/h, and the speed of car B is 50 km/h, then how many kilometers are the distance between A and B?
甲车从A地，乙车从B地同时相向而行，乙车到达A地后不停留立即返回，又在距B地140千米处追上甲车．已知甲车的速度是20千米/小时，乙车速度是50千米/小时，那么A、B两地相距多少千米．
<gadget id="calculator">140 / 20</gadget>
<output>7</output>

<gadget id="calculator">7 * 50</gadget>
<output>350</output>

<gadget id="calculator">350 - 140</gadget>
<output>210</output>

<result>210</result>