Two cars drive oppositely from two cities 400 kilometers apart at the same time. The speed of the car is 50 km/h and the speed of the truck is 40 km/h. After how many hours did the two cars meet?
两辆汽车同时从相距400千米的两城相对开出．汽车的速度是50千米/时，货车的速度是40千米/时．经过几小时两车相遇？
<gadget id="calculator">50 + 40</gadget>
<output>90</output>

<gadget id="calculator">400 / 90</gadget>
<output>40/9 = around 4.444444</output>

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