Calculating days in between 2 dates (which have after 14 days issued date)

Dear All,

Can someone help me with this.

Eg.

A B C D
IssuedDate DateClosed OpenCase (for current month; 14 days after issued date) OverdueCase (14 days after issued date exclude current month)
25/12/2012 28/12/2012 ? ?

I also include the example sheet here.

Detailed description:
OpenCase value is (DateClosed - IssuedDate) - exclude Sundays & Holidays for current month. And OpenCase counted also already due 14 days after the issued date.
OverdueCase value is sum of OpenCase of previous month (before 25th of the current month).

The range of submitting case is between 26th (this month) - 25th (next month).

I had try many formula using WEAKDAY function but can get any value.

Please someone help me on this.