The distance between the two docks is 140 kilometers. It takes 7 hours for a boat to sail along the current and 10 hours to sail against the current. What is the speed of the boat in still water?
两个码头相距140千米，一条船顺水行需7小时，逆水行需10小时，这条船在静水中的速度是多少．
<gadget id="calculator">140 / 7</gadget>
<output>20</output>

<gadget id="calculator">140 / 10</gadget>
<output>14</output>

<gadget id="calculator">20 + 14</gadget>
<output>34</output>

<gadget id="calculator">34 / 2</gadget>
<output>17</output>

<result>17</result>