The road from the foot of the mountain to the top is 15 kilometers long. Xiaohua walks 3 kilometers per hour up the mountain and 5 kilometers per hour down the mountain. How many kilometers per hour does he walk up and down the mountain on average?
从山脚到山顶的公路长15千米，小华上山每小时走3千米，下山每小时走5千米，他上、下山平均每小时走多少千米？
<gadget id="calculator">15 * 2</gadget>
<output>30</output>

<gadget id="calculator">15 / 3</gadget>
<output>5</output>

<gadget id="calculator">15 / 5</gadget>
<output>3</output>

<gadget id="calculator">5 + 3</gadget>
<output>8</output>

<gadget id="calculator">30 / 8</gadget>
<output>15/4 = around 3.75</output>

<result>15/4 = around 3.75</result>