The distance between A and B is 480 kilometers. Two trains leave opposite to each other at the same time. The express train travels 70 kilometers per hour, and the slow train travels 50 kilometers per hour. How many hours later will the two trains meet?
甲、乙两地相距480千米，两列火车同时从两地相对开出，快车每小时行70千米，慢车每小时行50千米，几小时后两车相遇？
<gadget id="calculator">70 + 50</gadget>
<output>120</output>

<gadget id="calculator">480 / 120</gadget>
<output>4</output>

<result>4</result>