It took Uncle Li to drive a truck from Foshan to Dongguan for 3 hours. The speed of the truck was 40 km/h, and it only took 2 hours to return. How many kilometers per hour did Uncle Li travel on average when he returned?
李叔叔开货车从佛山运货到东莞用了3小时，货车的速度是40千米/时，返回时只用了2小时，李叔叔返回时平均每小时行多少千米？
<gadget id="calculator">40 / 2</gadget>
<output>20</output>

<gadget id="calculator">3 * 20</gadget>
<output>60</output>

<result>60</result>