Example 4: The distance between A and B is 640 kilometers. Two cars drive from A to B at the same time. The first car travels 46 kilometers per hour, and the second car travels 34 kilometers per hour. The first car arrives at Return immediately after point B, how many hours did it take for the two cars to meet each other?
例4：甲、乙相距640千米，两辆汽车同时从甲地开往乙地，第一辆汽车每小时行46千米，第二辆汽车每小时行34千米，第一辆汽车到达乙地后立即返回，两辆汽车从开出到相遇共用了几小时？
<gadget id="calculator">46 + 34</gadget>
<output>80</output>

<gadget id="calculator">2 / 80</gadget>
<output>1/40 = around 0.025</output>

<gadget id="calculator">640 * (1/40)</gadget>
<output>16</output>

<result>16</result>