The length of the road between A and B is 180 km. A truck from A goes to B to purchase goods. It takes 4 hours to go and 5 hours to return. How many kilometers per hour does this truck travel on average for one round trip?
甲、乙两地间的公路长180千米．一辆甲地的卡车开往乙地采购货物，去时用了4小时，回来时用了5小时．这辆卡车往返一次平均每小时行多少千米？
<gadget id="calculator">180 * 2</gadget>
<output>360</output>

<gadget id="calculator">4 + 5</gadget>
<output>9</output>

<gadget id="calculator">360 / 9</gadget>
<output>40</output>

<result>40</result>