find time that employee work during the month

hallow,

i have problem that i have to find how much time employee work during the month but i have to consider month with holidays and so on what is the best way to do that?

example

if the standard hour for month is 180 hours and employee work just half month i wont to find the relative part of employee working in this month with consider the calendar of this moth (4 or 5 Sunday or more holidays).

Regards