Wang Ming climbs a mountain. He walks an average of 3 kilometers per hour when he goes up the mountain, and 4 kilometers per hour when he goes down the mountain. What is the average speed of Wang Ming when he climbs the mountain?
王明爬山，他上山时平均每小时走3千米，下山时平均每小时走4千米，那么王明爬山的平均速度是多少．
<gadget id="calculator">1 + 1</gadget>
<output>2</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(1/3) + (1/4)</gadget>
<output>7/12 = around 0.583333</output>

<gadget id="calculator">2 / (7/12)</gadget>
<output>24/7 = around 3.428571</output>

<result>24/7 = around 3.428571</result>