train of trucks and a train of passenger cars drive from City A to City B respectively. The trucks travel 40 kilometers per hour. Two hours after the trucks leave, the passenger cars depart from City A and travel 70 kilometers per hour. In order to ensure safety, two The distance between the workshops should not be less than 10 kilometers. According to this regulation, how many hours should the trucks stop at the latest to let the passenger cars pass?
一列货车和一列客车分别从甲城开往乙城，货车每小时行40千米，货车开出2小时后，客车才从甲城开出，每小时行70千米，为了保证安全，规定两车间的距离不应小于10千米，按此规定，货车最晚应该在开车后几小时停下来让客车通过？
<gadget id="calculator">40 * 2</gadget>
<output>80</output>

<gadget id="calculator">80 - 10</gadget>
<output>70</output>

<gadget id="calculator">70 - 40</gadget>
<output>30</output>

<gadget id="calculator">70 / 30</gadget>
<output>7/3 = around 2.333333</output>

<result>7/3 = around 2.333333</result>