Counting and summing the total number of overlapping days in two periods

I was interested to read the following post;

http://www.excelforum.com/excel-gene...end-dates.html

which checks to see if dates ovelap.

I have a similar problem but want the total number of days that overlap. So, for example...

If i have a week running from 06/08/12 to 12/08/12 (5 working days) and 3 people work 7 hours per day, that's a total of 3x7x5=105 hours.
If i have 2 people on holiday, one from 08/08/12 - 14/08/12 and the other from 06/08/12 to 10/08/12, I want to be able to calulate that I am losing 3x7+5x7=58 hours in this week (and a quantity in the following week too which will also need calulating. I have the following (see attachment).

Can you help, please?