Two cars drive from place A to place B at the same time. After 4 hours, car B is 20 kilometers behind car A. Car A travels 40 kilometers per hour. How many kilometers does car B travel per hour?
两辆汽车同时从甲地开往乙地，经过4小时后，乙车在甲车后面20千米，甲车每小时行驶40千米，乙车每小时行驶多少千米？
<gadget id="calculator">20 / 4</gadget>
<output>5</output>

<gadget id="calculator">40 - 5</gadget>
<output>35</output>

<result>35</result>