It takes Xiaoyun 4 hours to climb Qingyun Mountain. If it takes him 2.4 hours to go up the mountain, and the speed of going down the mountain is 7.5 kilometers per hour on the original road, what is his speed in kilometers per hour?
小云爬青云山，上下山共用4小时，如果他上山用了2.4小时，按原路下山速度每小时7.5千米，他上山的速度是多少千米/时．
<gadget id="calculator">4 - 2.4</gadget>
<output>1.6</output>

<gadget id="calculator">1.6 / 2.4</gadget>
<output>0.666667</output>

<gadget id="calculator">7.5 * 0.666667</gadget>
<output>5.000002</output>

<result>5.000002</result>