Uncle Wang went from home to the county town to pull fertilizer. It took him 4 hours to travel 45 kilometers per hour when he went there, and 6 hours to return. How many kilometers per hour did he travel on average when he returned?
王叔叔从家去县城拉化肥，去时每小时行45千米，用了4小时，回来时用了6小时，返回时平均每小时行多少千米？
<gadget id="calculator">4 / 6</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">45 * (2/3)</gadget>
<output>30</output>

<result>30</result>