[SOLVED] workday function --> calculate START date

Hello,

The workday function can return the end date based on start date and duration, excluding weekends. However, I want to calculate start date based on end date and duration also weekends.

For example

Start Date: ?
Finish Date: 27 Jul 2010
Duration: 3 days

The Start Date should be 24 July 2010

I would very much appreciate it if you would take a look at this problem, many thanks in advance for your help!

Regards,

Kaatje