An express train and a slow train are traveling towards each other at the same time from two places 500 km apart. It is known that the fast train travels 70 kilometers per hour and the slow train travels 55 kilometers per hour. How long does it take for the two vehicles to meet?
一列快车和一列慢车同时从相距500千米的两地相向而行．已知快车每时行70千米，慢车每时行55千米，经过多少时两车相遇？
<gadget id="calculator">70 + 55</gadget>
<output>125</output>

<gadget id="calculator">500 / 125</gadget>
<output>4</output>

<result>4</result>