A train travels from A to B at 80 kilometers per hour and can be reached in 12 hours; now if the speed of this train is increased to 4 times, how many hours can it arrive in advance?
一列火车从甲地开往乙地，每小时行80千米，12小时可以到达；现在把这列火车的速度增加到4倍，可以提前几小时到达？
<gadget id="calculator">80 * 12</gadget>
<output>960</output>

<gadget id="calculator">80 * 4</gadget>
<output>320</output>

<gadget id="calculator">960 / 320</gadget>
<output>3</output>

<gadget id="calculator">12 - 3</gadget>
<output>9</output>

<result>9</result>