The distance between the two piers is 231 kilometers, and it takes 11 hours for the ship to travel along the river, which is 10 kilometers less per hour against the current than along the river. So how many more hours will it take to drive this distance against the current than with the downstream?
两码头相距231千米，轮船顺水行驶这段路需要11小时，逆水比顺水每小时少行10千米．那么行驶这段路程逆水要比顺水需要多用多少小时？
<gadget id="calculator">231 / 11</gadget>
<output>21</output>

<gadget id="calculator">21 - 10</gadget>
<output>11</output>

<gadget id="calculator">21 - 11</gadget>
<output>10</output>

<result>10</result>