A team is 450 meters long and advances at a speed of 2 meters per second. How many minutes does it take for a person to rush from the tail of the team to the front of the team at a speed of 3 meters per second, and then return to the back of the team?
一支队伍长450米，以每秒2米的速度前进，一个人以每秒3米的速度从队尾赶到队伍的最前面，然后再返回队尾，一共用了多少分钟．
<result>9</result>