The distance between A and B is 450 kilometers. Two trains depart from A and B at the same time. A train travels 55 kilometers per hour, and B travels 45 kilometers per hour. How many hours later will the two trains meet?
甲、乙两地相距450千米，两列火车同时从甲、乙两地相对开出，甲车每小时行55千米，乙车每小时行45千米，几小时后两车相遇？
<gadget id="calculator">55 + 45</gadget>
<output>100</output>

<gadget id="calculator">450 / 100</gadget>
<output>9/2 = around 4.5</output>

<result>9/2 = around 4.5</result>