There are 12 hours from 9 AM to 9 PM. This includes the full hours from 10 AM to 9 PM, plus the hour from 9 AM to 10 AM. Therefore, the total duration is 12 hours.
12 hours.
From 9am to 6:30pm is 9 hours and 30 minutes.
21
21 hours
6 hours
5 Hours
There are zero hours between 9 am and 9 am.
11 hours
5.7
Twelve hours
21
20