Hua Ming rode a racing car at 15km per hour and arrived at the destination in 6 hours. If it takes 5 hours to arrive, how many kilometers per hour? (Solve with ratio)
华明骑赛车每小时行15km，6小时到达目的地．如果5小时到达，每小时行多少km？(用比例解)
<gadget id="calculator">15 * 6</gadget>
<output>90</output>

<gadget id="calculator">90 / 5</gadget>
<output>18</output>

<result>18</result>