If a small boat travels at a speed of 25 kilometers per hour in still water and travels along a 210-kilometer river in 6 hours, how many hours will it take to return to the original place?
一只小船在静水中速度为每小时25千米，在210千米的河流中顺水而行时用了6小时，则返回原处需用多少小时．
<gadget id="calculator">210 / 6</gadget>
<output>35</output>

<gadget id="calculator">35 - 25</gadget>
<output>10</output>

<gadget id="calculator">25 - 10</gadget>
<output>15</output>

<gadget id="calculator">210 / 15</gadget>
<output>14</output>

<result>14</result>