The road between A and B is divided into uphill and downhill sections, a total of 70 kilometers. Lan Lan’s uphill speed is 5 km/h, and the downhill speed is 7 km/h. 10.5 hours, how many hours will it take to return.
A、B两地之间的道路分上坡和下坡两种路段，共70千米，兰兰上坡速度为5千米/时，下坡速度为7千米/时，去时用了10.5小时，则返回时用多少小时．
<gadget id="calculator">70 / 5</gadget>
<output>14</output>

<gadget id="calculator">70 / 7</gadget>
<output>10</output>

<gadget id="calculator">10 - 10.5</gadget>
<output>-0.5</output>

<gadget id="calculator">14 + (-0.5)</gadget>
<output>13.5</output>

<result>13.5</result>