Two cars A and B are traveling towards each other from two places at the same time. Car A travels 45 kilometers per hour and car B travels 42 kilometers per hour. The two cars meet at a distance of 12 kilometers from the midpoint. How many hours did it take for the two cars to meet after they drove out at the same time?
甲乙两辆汽车同时从两地相向而行，甲车每小时行45千米，乙车每小时行42千米．两车在距离中点12千米处相遇．两车同时开出后经过多少小时相遇？
<gadget id="calculator">45 - 42</gadget>
<output>3</output>

<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">12 * (2/3)</gadget>
<output>8</output>

<result>8</result>