The railway from Beijing to Tianjin is about 138 kilometers long. A train runs from Beijing to Tianjin and returns to Beijing after a 2-hour break. It takes 6 hours. How many kilometers per hour does the train travel on average?
北京到天津的铁路大约长138千米，一列火车从北京开到天津，休息2小时后又返回北京，共用了6小时．这列火车平均每小时行多少千米？
<gadget id="calculator">6 - 2</gadget>
<output>4</output>

<gadget id="calculator">2 / 4</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">138 * (1/2)</gadget>
<output>69</output>

<result>69</result>