In 2015, there were approximately 33,100 firearm fatalities (homicides and suicides). express this quantity in deaths per hour

The data given is for the whole year of 2015, so time duration is 1 year.Convert 1 year into units of hours:
1 year = 365 days 
time = 365 days * (24 hours / day) = 8760 hours

Therefore the deaths per hour is:
fatality = 33,100 / 8760 hours 
fatality = 3.78 per hour