The railway from Wuhan to Beijing is about 1620 kilometers long. An express train runs from Wuhan to Beijing, traveling an average of 105 kilometers per hour. At the same time, a slow train runs from Beijing to Wuhan. After 9 hours, the two trains meet. How many kilometers per hour does the slow train travel on average?
武汉到北京的铁路长约1620千米．一列快车从武汉开往北京，平均每小时行105千米，同时有一列慢车从北京开往武汉，经过9小时两车相遇．慢车平均每小时行多少千米？
<gadget id="calculator">1_620 / 9</gadget>
<output>180</output>

<gadget id="calculator">180 - 105</gadget>
<output>75</output>

<result>75</result>