The distance between A and B is 510 kilometers. Two cars drive from the two places at the same time. Car A travels 90 kilometers per hour. After 3 hours, the two cars meet. How many kilometers does car B travel per hour?
甲乙两地相距510千米，两车从两地同时相对开出，甲车每小时行90千米，3小时后两车相遇．求乙车每小时行多少千米？
<gadget id="calculator">510 / 3</gadget>
<output>170</output>

<gadget id="calculator">170 - 90</gadget>
<output>80</output>

<result>80</result>