Treatment of Sundays and other Public Holidays while calculating salary for of a pvt firm in Kolkata

Dear Sir(s)
My question is very simple. Lets take this month - January 2019-
4 sundays, 1 holiday (26th Jan), total days in month 31. An employee getting salary 12000 /- ( no deduction what so ever). How much salary he is entitled to get ? for the month shall we take 31 days ofr 31-4 sundays -1 holiday = 26 days and divide 12000/- by it ? I want to know the rule, pls..
It is a partnership chartered accountants firm. Pls igore my earlier thread # 1
Regards,
Dev Chowdhury

Dear Dev,
A C.A's firm is an establishment under the State Shops and Establishments Act. Therefore,the seventh day following six days of work should be a paid weekly holiday. Similarly, 26th January every year is a paid National holiday on a/c of the Republic day.
Besides, the universal practice for accounting purpose by convention is treating a month as a period comprising of 30 days only.