It is 4 hours.
18½ hours
3 hours.
18½ hours
9 hours 30 minutes
2 hours and 30 minutes.
9 hours and 30 minutes.
5 and a half
7
Eight and one half hours.
1230
three and a half 19:30 - 16:00 = 03:30
10:30 to 3:30 is five hours.