7:45 am to 6:15 pm is 10 hours 15 minutes (101/4 hours)
9 hours, 45 minutes
10 hours and 45 minutes.
61/2 + 24n hours where n is an integer.
From 8am to 6:15pm is 10 hours and 15 minutes.
There are 10.25+24k where k is an integer.
6:15am to 5pm is 10 hours and 45 minutes.
8.5 + 24k hours where k is any integer.
From 6:15am to 1:30pm is 7 hours and 15 minutes.
10 hrs
There are 9 and 1/2 hours between 8:45 am and 6:15 pm.
There are 35 minutes
IF they're both on the same day, then they're 5hours 10minutes apart.