The bus from Hengyang to Guilin, if the speed is 80 kilometers per hour, it will arrive at Guilin on time, if the speed is 100 kilometers per hour, it will enter the station one hour earlier, how many kilometers is it from Hengyang to Guilin?
衡阳至桂林客车，如果每小时80千米速度前进正好正点到达桂林，如果每小时100千米速度前进，则提前一个小时进站，问衡阳到桂林多少千米？
<gadget id="calculator">1 / 80</gadget>
<output>1/80 = around 0.0125</output>

<gadget id="calculator">1 / 100</gadget>
<output>1/100 = around 0.01</output>

<gadget id="calculator">(1/80) - (1/100)</gadget>
<output>1/400 = around 0.0025</output>

<gadget id="calculator">1 / (1/400)</gadget>
<output>400</output>

<result>400</result>