Xiaohong's house is 252 kilometers away from grandpa's house. If you take a bus, the speed is 42 kilometers per hour. If you go by train, the speed is 84 kilometers per hour. How much time is saved by train compared to bus?
小红家距爷爷家252千米，如果坐客车去，速度是每小时42千米．如果坐火车去，速度是每小时84千米．从火车比坐客车节省多少时间？
<gadget id="calculator">252 / 42</gadget>
<output>6</output>

<gadget id="calculator">252 / 84</gadget>
<output>3</output>

<gadget id="calculator">6 - 3</gadget>
<output>3</output>

<result>3</result>