A ship travels from A to B. It takes 4 hours to go and 7 hours to return. The distance between A and B is 140 kilometers. How much more kilometers does it travel per hour than the return?
一艘轮船从甲地开往乙地，去时用4小时，返回用7小时，甲乙两地相距140千米，问去时每小时比返回每小时多行多少千米？
<gadget id="calculator">140 / 4</gadget>
<output>35</output>

<gadget id="calculator">140 / 7</gadget>
<output>20</output>

<gadget id="calculator">35 - 20</gadget>
<output>15</output>

<result>15</result>