Hi, I need to calculate the no.of.working day ?

I need to calculate the no.of.working day in a month with weekends also for 7 days.?
i) Available of leave is 4 days in a monthly, if he is taking more than 4 days that must go to loss pay should be ,minus from his annual salary.
ii) if he is taking less than 4 days. if the leave taken must be deduction the available leave. The value should not be negative.