There are willow trees planted every 9 meters on one side of the road. Zhang Jun drove for 5 minutes and saw 201 trees. He asked how many kilometers per hour the car traveled?
马路的一边每隔9米栽有一棵柳树，张军乘坐5分钟看到了201棵树，问汽车每小时行多少千米？
<result>21.6</result>