Two cars, A and B, drive from point A to point B at the same time. Their speeds are 42km/h and 38km/h respectively. After arriving at point B, car A returns immediately and meets car B at a distance of 20km from point B. The distance between A and B.
甲、乙两辆汽车同时从A地开往B地，它们的速度分别是42km/h、38km/h，甲车到达B地后立即返回，在距离B地20km的地方与乙车相遇，求A、B两地的距离．
<gadget id="calculator">42 - 38</gadget>
<output>4</output>

<gadget id="calculator">2 / 4</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">20 * (1/2)</gadget>
<output>10</output>

<gadget id="calculator">42 * 10</gadget>
<output>420</output>

<gadget id="calculator">420 - 20</gadget>
<output>400</output>

<result>400</result>