There are (7.5 + 24k) hours where k is an integer.
12 hours
9 hours.
8
6 hours and 30 minutes.
9h 15m
4 hours and 15 minutes.
10 & 1/2
it is 1 hour 30 mins = 1½ hours.
12pm - 9am = 3 hours; 12:30 - 9:30 = 3 hours
930
At an average 60 mph: 15 and 1/2 hours