> Because 40 hours a week are, if you remove vacations, holidays and sick leaves, on average roughly 4 hours per day.

I'm sorry, but who told you this?

The median amount of PTO in American companies is 10 days + 8 days of Federal holidays. That 18 days vs 260 weekdays, or 7% of the work year, meaning the average American works 7.5 hours a day, not 4.