On the highway, a truck is traveling at 42 kilometers per hour. At 21 kilometers away from the truck, a car is catching up at 49 kilometers per hour. A few hours later, it is on the way Caught up with the truck?
在公路上，一辆卡车正以每小时42千米的速度向前行驶，在离卡车21千米的地方，一辆小汽车正以每小时49千米的速度赶上来，几小时后在途中追上了卡车？
<gadget id="calculator">49 - 42</gadget>
<output>7</output>

<gadget id="calculator">21 / 7</gadget>
<output>3</output>

<result>3</result>