In the quality practice activities, the astronomy team observes the meteor shower phenomenon for the first time at 9:00 in the morning, and then observes every 4 hours. When he observes for the tenth time, what is the angle between the hour hand and the minute hand?
在素质实践活动中，天文小组观察流星雨现象，从上午九点第一次观察，以后每隔4小时观察一次，当他第十次观察时，时针与分针的夹角是多少度．
<result>90</result>