The distance between A and B is 500 kilometers. A bus and a truck drive from A to B at the same time. When the bus arrives at B, the truck only travels 400 kilometers and continues to drive for 2 hours to reach B. How many hours does the bus take to complete the journey.
甲、乙两地相距500千米，客车和货车同时由甲地开往乙地，当客车到达乙地时，货车只行了400千米，继续行驶2小时才能到乙地．客车行完全程需要多少小时．
<gadget id="calculator">500 - 400</gadget>
<output>100</output>

<gadget id="calculator">100 / 2</gadget>
<output>50</output>

<gadget id="calculator">400 / 50</gadget>
<output>8</output>

<result>8</result>