Xiaotian arrives at school at 8:20 a.m. and ends at 11:50 noon. He arrives at school at 2:00 p.m. and ends at 16:30. How long does Xiaotian stay at school every day?
小天每天上午8：20到校，中午11：50放学，下午2：00到校，16：30放学，小天每天在校多长时间？
<result>6</result>