Two cars drive from a tollbooth to the same place at the same time. The passenger car travels 84 kilometers per hour, and the truck travels 68 kilometers per hour. After 4 hours, how many kilometers are there between the truck and the passenger car?
两辆汽车同时从一个收费站出发向同一地点开车，客车每小时行84千米，货车每小时行68千米，4小时后，货车与客车相距多少千米？
<gadget id="calculator">84 - 68</gadget>
<output>16</output>

<gadget id="calculator">16 * 4</gadget>
<output>64</output>

<result>64</result>