A ship sailed 36 kilometers downstream in 2 hours. If the speed of still water is 12 kilometers per hour, what is the speed of water in kilometers per hour?
某船在水中顺流航行了36千米，用时2小时．如果静水速度为每小时12千米，则水流速度为每小时多少千米．
<gadget id="calculator">36 / 2</gadget>
<output>18</output>

<gadget id="calculator">18 - 12</gadget>
<output>6</output>

<result>6</result>