A person goes up a mountain, travels 4 kilometers per hour, and arrives in 3 hours. When going down the mountain by the same route, he travels 6 kilometers per hour. What is the average speed of this person going up and down the hill?
有一个人上一座山，每小时行4千米，3小时到达，按原路下山时，每小时行6千米．这个人上山、下山的平均速度是多少？
<gadget id="calculator">4 * 3</gadget>
<output>12</output>

<gadget id="calculator">12 / 6</gadget>
<output>2</output>

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

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">12 * (2/5)</gadget>
<output>24/5 = around 4.8</output>

<result>24/5 = around 4.8</result>