Two cars, A and B, drive from two places 630 kilometers apart at the same time, and they meet after 4.2 hours. It is known that car A travels 70 kilometers per hour, how many kilometers per hour does car B travel?
甲乙两辆汽车同时从相距630千米的两地相对开出，经过4.2小时两车相遇．已知甲车每小时行70千米，乙车每小时行多少千米？
<gadget id="calculator">630 / 4.2</gadget>
<output>150</output>

<gadget id="calculator">150 - 70</gadget>
<output>80</output>

<result>80</result>