From point A to point B, car A takes 6 hours and car B takes 10 hours. Two cars depart from A to B at the same time, and A returns immediately after arriving at B. How many hours did the two cars meet after departure?
从A地到B地，甲车需6小时，乙车需10小时．两车同时从A地出发到B地，甲车到达B地后立即返回．两车出发后几小时相遇？
<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(1/6) + (1/10)</gadget>
<output>4/15 = around 0.266667</output>

<gadget id="calculator">2 / (4/15)</gadget>
<output>15/2 = around 7.5</output>

<result>15/2 = around 7.5</result>