How to calculate workdays

Dear excel forum,

i have problem in calculating wordays
commonly, there are 5 workdays in a week.
What about 6 days? Because my offday just on friday.
Count
start day 01/10/2013 sunday ?
End day 31/10/2013 monday ?
Tuesday ?
Holiday 14/10/2013 wednesday ?
15/10/2013 thursday ?
Friday ?
Saturday ?

Offday=saturday,sunday
workday 21

offday=friday
workday ???
LIKE IN ATTACHMENT

Thank you!