If the speed of a boat in still water is 13.5 kilometers per hour, the speed of the current is 3.5 kilometers per hour, what is the speed of the boat going against the current in kilometers per hour?
某船在静水中的速度是每小时13.5千米，水流速度是每小时3.5千米，逆水而行的速度是每小时多少千米．
<gadget id="calculator">13.5 - 3.5</gadget>
<output>10</output>

<result>10</result>