1. Read Part XII and Section 60I of the EA at Section 60I
2. Since it is monthly rated salary, use number of days of the month will be more accurate. You may of course use 26 as long as it gives you the correct amount and it is not less than that calculated using calendar month.
3. No such provision, just simple arithmetic. For example, salary per month RM1500, the month in September has 30 days, or October has 31 days, so, the per day salary is = ?