If we’re talking about two random weeks, then it’s very simple. You only need to account for possible start of the year and end of the year incomplete weeks.
Otherwise, any week in between is a full week: 7 days total minus the 2 days week-end.
33: 5 days
34: 5 days
35: 5 days
36: 5 days
20 days total. Of course, you need to count down the legal holidays.
Unless you mean something else. Like between two random dates.