1 week is 7 days.
3 weeks = 21 days. Answer D. is correct.
A hour is 3600 seconds
24 hours ( a day ) is 86400 seconds
21 days is 1814400 seconds. * This is not an option *
Since 24 hours are in a day 24 hours x 21 days is 504 hours
Answer A. is correct
504 hours x 60 minutes per hour is 30240
Answer B. is correct. These are all the correct answers, A,B, and D.