The distance between the two cities of AB is 450 kilometers, and two cars drive from city A to city B at the same time. The first car travels 45 kilometers per hour, and the second car travels 30 kilometers per hour. After the first car arrives at City B, it returns immediately. How many hours did it take for the two cars to meet each other?
AB两城之间的路程是450千米，两辆汽车同时从A城开往B城．第一辆汽车每小时行45千米，第二辆汽车每小时行30千米，第一辆汽车到达B城后，立即返回，两辆车从开出到相遇，共用了多少小时．
<gadget id="calculator">45 + 30</gadget>
<output>75</output>

<gadget id="calculator">2 / 75</gadget>
<output>2/75 = around 0.026667</output>

<gadget id="calculator">450 * (2/75)</gadget>
<output>12</output>

<result>12</result>