The distance between A and B is 840 kilometers. Two trains depart from A and B at the same time and meet each other 4 hours later. The speed of car A is 100 km/h, how many kilometers per hour does car B travel?
甲，乙两地相距840千米，两列火车分别从A、B两地同时相对开出，4小时后相遇．甲车的速度是100千米/时，求乙车每小时行多少千米？
<gadget id="calculator">840 / 4</gadget>
<output>210</output>

<gadget id="calculator">210 - 100</gadget>
<output>110</output>

<result>110</result>