It took Uncle Li 6 hours to drive the truck from Kunming to Dali. The speed of the truck was 40 km/h, and it only took 4 hours to return. How many kilometers per hour did Uncle Li drive on average when he returned?
李叔叔开货车从昆明运货到大理用了6小时，货车的速度是40千米/时，返回时只用了4小时，李叔叔返回时平均每小时行驶多少千米？
<gadget id="calculator">6 / 4</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">40 * (3/2)</gadget>
<output>60</output>

<result>60</result>