The distance between the two places is 280 kilometers. The speed of the ship in still water is 17 kilometers per hour, and the speed of flowing water is 3 kilometers per hour. How many hours does it take for the ship to go back and forth between the two places?
两地相距280千米，轮船在静水的速度是每小时17千米，流水速度每小时3千米，轮船在两地来回一次需要多少小时．
<gadget id="calculator">17 + 3</gadget>
<output>20</output>

<gadget id="calculator">280 / 20</gadget>
<output>14</output>

<gadget id="calculator">17 - 3</gadget>
<output>14</output>

<gadget id="calculator">280 / 14</gadget>
<output>20</output>

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

<result>34</result>