A train is 450 meters long and has to pass through a cave with a length of 6750 meters. At 9:59 the front of the train exited the cave, and at 10:02 the rear of the train passed through the cave. What is the speed of the train in kilometers per hour?
一列火车长450米，要穿过一个长6750米的山洞．9：59火车车头在山洞出口，10：02火车车尾全部通过山洞．火车的速度是每小时多少千米？
<gadget id="calculator">450 + 6_750</gadget>
<output>7_200</output>

<gadget id="calculator">3 / 60</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">7_200 / 1_000 / (1/20)</gadget>
<output>144</output>

<result>144</result>