Three hours.
8580 seconds
12,300 seconds.
There are 24 times 7 times 3, or 504 hours in three weeks. Multiply by 60 to get minutes, 30240, and by 60 again to get seconds, 1814400.
122400 seconds
12,600 seconds.
11,130 seconds.
Three hours is 180 minutes, and 10800 seconds and 1/8 days.
11250 (Search Google for "3 1/8 hours in seconds")
11,250
10,920 secs
Not sure if you want seconds in 3 and 1/2 hours or in three 1/2 hours. If it is the first case then 1 hour is 3600 seconds, hence 3 hours is 10800 seconds. Add to this the number of seconds in half hour which is 1800 to get a total of 12600 seconds If it is the second case then 1/2 hour is 1800 seconds, hence 3 half hours is 5400 seconds.
60 X 60 X 3 = 10,800
1760400 seconds
3500 seconds = 3500/3600 hours = 0.9722... hours.
22.0 seconds = 0.006111... hours.
37800 seconds = 10.5 hours