It is 24 kilometers from the foot of the mountain to the top of the mountain. A person goes up the mountain at a speed of 4 kilometers per hour, and he immediately goes down the mountain from the original road. It is known that the average speed of going up and down the mountain is 6 kilometers. How many kilometers per hour does this person travel down the mountain?
山脚到山顶有24千米．一个人以每小时4千米的速度上山，他立即从原路下山，已知上山和下山的平均速度是6千米．这人下山每小时行多少千米？
<gadget id="calculator">2 / 6</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">24 * (1/3)</gadget>
<output>8</output>

<gadget id="calculator">24 / 4</gadget>
<output>6</output>

<gadget id="calculator">8 - 6</gadget>
<output>2</output>

<gadget id="calculator">24 / 2</gadget>
<output>12</output>

<result>12</result>