From city A to city B, car A takes 10 hours; from city B to city A, car B takes 15 hours. If two cars depart from two cities at the same time, how many hours will they meet?
从A城到B城，甲车要10小时；从B城到A城，乙车要15小时．若两车同时分别从两城出发，几小时后相遇？
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(1/10) + (1/15)</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">1 / (1/6)</gadget>
<output>6</output>

<result>6</result>