Formula to Compute Overtime hours

I have a document which is set up like a calendar. It is used to calculate
an employee's work hours per month. It is also used to calculate any
additional duties they work during work days or on days off. This document
is already set up for these calculations.

I now want it to tell me, on work days only, how much time an employee
spends working particular duties when it exceeds their normal work hours
(this is chosen by the user using a drop down list to choose their
appropriate work hours - could be between 8 and 12 hours). I'm looking to
capture this information for a month.


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 (this indicates the days of the
w w w w w (w=workday,
blank=day off)
12 3 4 13 2 1 10 7 (number of hours
working each DOM)

Normal work hours: 9 (user input from drop

In this example, this employee's normal work schedule is 9 hours a day. I
am looking for a formula which will add the overage (3 hours for the 1st and
4 hours for the 6th). I don't want to capture any amount which is equal or
less than 9 hours. However, if the user were to use the drop down to show
their hourly day as 10 hours, I would be looking to capture the same
information as shown above (2 hours for the 1st and 3 hours for the 6th).

Thanks very much in advance.