There are 60 minutes in an hour, therefore: 
 
 Breaths per hour = 12 X 60, 15 X 60 
 = 720 to 900 breaths per hour 
 
 There are 24 hours in a day, therefore: 
 
 Breaths per day = 720 X 24, 900 X 24 
 = 17,280 to 21,600 breaths per day.
This differs between adults and kids, so:
A child breathes around 28,800 times a day.
An Adult breathes around 23040 times a day.
Hope this helps!