The railway line from Beijing to Hohhot is 660 kilometers long. One train departs from Hohhot and travels 48 kilometers per hour; the other train departs from Beijing and travels 72 kilometers per hour. Two trains leave at the same time, going towards each other, when will they meet?
北京到呼和浩特的铁路线长660千米，一列火车从呼和浩特开出，每小时行驶48千米；另一列火车从北京开出，每小时行驶72千米．两列火车同时开出，相向而行，经过几时相遇？
<gadget id="calculator">48 + 72</gadget>
<output>120</output>

<gadget id="calculator">660 / 120</gadget>
<output>11/2 = around 5.5</output>

<result>11/2 = around 5.5</result>