Two trains depart from two cities 600 kilometers apart at the same time. One train travels 60 kilometers per hour and the other train travels 75 kilometers per hour. After how many hours did we meet?
两列火车从相距600千米的两城同时相对开出．一列火车每小时行60千米，另一列火车每小时行75千米．经过几小时相遇？
<gadget id="calculator">60 + 75</gadget>
<output>135</output>

<gadget id="calculator">600 / 135</gadget>
<output>40/9 = around 4.444444</output>

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