Cars A and B start at the same time from two places 30 kilometers apart and drive in the same direction. Car B is in front at 6 kilometers per hour, and car A is driving behind at 12 kilometers per hour. It takes several hours for A to catch up with B. ?
甲乙两车同时从相距30千米的两地同时出发同向而行，乙车在前，每小时6千米，甲车在后行车，每小时12千米，甲经过几小时才能追上乙？
<gadget id="calculator">12 - 6</gadget>
<output>6</output>

<gadget id="calculator">30 / 6</gadget>
<output>5</output>

<result>5</result>