Uncle Wang went to climb the mountain on Sunday. He said that it took him 3 hours to go up the mountain, walking 2.8 kilometers per hour, and only 2 hours to go down the mountain along the original road. How many kilometers per hour does Uncle Wang walk up and down the mountain on average?
王叔叔星期天去爬山，说他上山用了3小时，每小时走2.8千米，沿原路下山仅用了2小时．王叔叔上下山平均每时走多少千米？
<gadget id="calculator">2.8 * 3 * 2</gadget>
<output>16.8</output>

<gadget id="calculator">3 + 2</gadget>
<output>5</output>

<gadget id="calculator">16.8 / 5</gadget>
<output>3.36</output>

<result>3.36</result>