Ding Ding arrives at school at 7:30 in the morning, eats at school at noon, and leaves school at 4:30 in the afternoon. How many hours does he spend in school a day?
丁丁早上7：30分到校，中午在学校吃饭，下午4：30放学，他一天在校时间为多少小时．
<result>9</result>