The expressway from Nanjing to Shanghai is 360 kilometers long. It takes 4 hours for a passenger car to travel from Nanjing to Shanghai, and 5 hours for a truck to travel from Shanghai to Nanjing. When two vehicles leave opposite each other at the same time, how many hours will they meet?
南京到上海的高速公路长360千米，一辆客车从南京到上海需要4小时到达，一辆货车从上海到南京需要5小时到达，两辆车同时从两地相对开出，几小时相遇？
<gadget id="calculator">40 / 9</gadget>
<output>40/9 = around 4.444444</output>

<result>40/9 = around 4.444444</result>