how to compute difference in date/time vs today excluding weekend, holidays, and non-work hours? I'm computing the age of incident ticket from the time it was created and today.

Column A = Creation Date
Column B = Difference in date/time (should be in days)
Business Hours is from 09:00-18:00
Column C = Holidays (from C2-C12)

like for example:

Column A = 08/12/2015 10:58:05
Today's Date = 08/13/2015 10:58:05
Column B = 0.333 days (8 hours/24 hours)

Please help. Thanks!