MONTHDAYCOUNT 
Returns the number of the specified weekdays in the provided month
js
MONTHDAYCOUNT(year_number, month_number, week_day)Parameters 
year_number- The year.month_number- The month (1-12).week_day- The week day (Mon, Tue, Wed, Thu, Fri, Sat, Sun).
Examples 
js
MONTHDAYCOUNT(2021, 12, "Mon")Result: 4