1 year = 365 days
42 days = 1.4 months holidays
12 - 1.4 = 10.6 months of work
900/10.6 = 85 hrs/month
So when you work you would potentially "feel" 85 hours if you work 900 hrs year.
But yes, 900 over the WHOLE year is 75. Just giving you a different angle.