The road between A and B is 240 kilometers long. A car can travel an average of 80 kilometers per hour on a highway, but can only travel an average of 40 kilometers per hour on an ordinary road. How much time does it take for this car to travel from city A to city B by taking the expressway instead of taking the ordinary road?
甲乙两个城市之间的公路长240千米．一辆汽车在高速公路上平均每小时可行驶80千米，在普通公路上平均每小时只能行驶40千米．这辆汽车从甲市到乙市走高速公路要比走普通公路节省多少时间？
<gadget id="calculator">240 / 40</gadget>
<output>6</output>

<gadget id="calculator">240 / 80</gadget>
<output>3</output>

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

<result>3</result>