The railway from Changsha to Guangzhou is 699 kilometers long. A freight train travels 69 kilometers per hour from Changsha to Guangzhou. One hour after the freight train leaves, a passenger train departs from Guangzhou to Changsha and travels 71 kilometers per hour. How many hours later will the two cars meet?
长沙到广州的铁路长699千米，一列货车从长沙开往广州，每小时行69千米，这列货车开出1小时后，一列客车从广州出发开往长沙，每小时行71千米，再过几小时后两车相遇？
<gadget id="calculator">699 - 69</gadget>
<output>630</output>

<gadget id="calculator">69 + 71</gadget>
<output>140</output>

<gadget id="calculator">630 / 140</gadget>
<output>9/2 = around 4.5</output>

<result>9/2 = around 4.5</result>