You can put this solution on YOUR website! 7:21 am is equal to 7:21 in 24 hours time.
3:30 pm is equal to 15:30 in 24 hour time.
15 - 7 = 8 hours.
30 - 21 = 9 minutes.
you worked for 8 hours and 9 minutes.
if you want to keep am and pm time, then do the following:
from noon to 3:30 pm is 3 hours and 30 minutes.
from 7:21 am to noon is 4 hours and 39 minutes.
add up 3 hours and 30 minute sand 4 hours and 39 minutes and you get 7 hours and 69 minutes which then translates to 8 hours and 9 minutes.