A small car with a speed of 80 kilometers per hour and a large truck with a speed of 40 kilometers per hour travel from point A to point B on the same road. If the large truck leaves for 3 hours first, how many hours does the small car pass by? Can catch up with large trucks.
一辆速度是每小时80千米的小汽车和一辆速度是每小时40千米的大货车由同一条公路从A地前往B地，如果大货车先出发3小时，那么小汽车经过多少小时可以追上大货车．
<gadget id="calculator">40 * 3</gadget>
<output>120</output>

<gadget id="calculator">80 - 40</gadget>
<output>40</output>

<gadget id="calculator">120 / 40</gadget>
<output>3</output>

<result>3</result>