Uncle Zhang did mountaineering training. It took him 5 hours and 24 minutes to go up the mountain, with an average of 4 kilometers per hour. It took only 4 hours and 30 minutes to return. Ask him how many kilometers per hour he travels on average when he returns?
张叔叔进行登山训练，上山时用了5小时24分，平均每小时4千米．返回时只用了4小时30分．求他返回时平均每小时行多少千米？
<gadget id="calculator">5.4 / 4.5</gadget>
<output>1.2</output>

<gadget id="calculator">4 * 1.2</gadget>
<output>4.8</output>

<result>4.8</result>