60 seconds = 1 minute so 8400 seconds = 8400/60 = 140 minutes. Simple!
3600 sec per hour, 60 sec per minute. 3600 x 2 + 60 x 20 = 8400
6 minutes, 11 seconds
3 minutes and 32 seconds
7 minutes, 28 seconds
12 minutes 51 seconds
3 minutes 23 seconds
Six minutes, seven seconds.
8 minutes, 51 seconds
There are 5 minutes and 50 seconds
3 minutes 2 seconds
11 minutes, 10 seconds.
7 minutes, 30 seconds.