person climbs a mountain along a road 12 kilometers long, and then descends the same road. The speed when going up the mountain is 2 kilometers per hour; the speed when going down the mountain is 6 kilometers per hour. So, what is his average speed in kilometers per hour during the whole process of going up and down the mountain?
某人沿一条长为12千米的路上山，又从原路下山．上山时的速度是每小时2千米；下山时的速度是每小时6千米．那么，他在上、下山全过程中的平均速度是每小时多少千米？
<gadget id="calculator">12 * 2</gadget>
<output>24</output>

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

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

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

<gadget id="calculator">24 / 8</gadget>
<output>3</output>

<result>3</result>