When subtracting hours from time, start by placing the hour value of the time on a number line that goes from 1 to 12. Move left on the number line for each hour you are subtracting and when you pass 1, go back to 12 and change the period from AM to PM or PM to AM.
For example, if you are subtracting 6 hours from 2:45 AM

- Start at 2 on the number line
- Move 3 spots to the left so you pass 1
- Go forward to 12 and change the period from AM to PM
- Move left the remaining 4 spots
- 6 hours before 2:45 AM is 8:45 PM