A train travels from A to B. If it travels 180 kilometers per hour and arrives in 4 hours, if it arrives in 6 hours, how much less kilometers does it need to travel per hour?
一列火车从甲地开往乙地，如果每小时行180千米，4小时到达，如果6小时到达，每小时需少行驶多少千米？
<gadget id="calculator">4 / 6</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">180 * (2/3)</gadget>
<output>120</output>

<gadget id="calculator">180 - 120</gadget>
<output>60</output>

<result>60</result>