Trying to calculate how many days my project takes

Hello everyone,

Context : I am trying to calculate how many days one task, and a whole project (which is a compilation of many tasks) takes to be done. The difficulty here is that I need to exclude in the days the hours that are not worked. We assume that we are working between 9:00 and 19:00, which makes 10 worked hours a day. We also assume that we are not working on Sundays.

Knowing this, I have 3 different columns :

  1. The first tells the date and hour of the beginning of a task
  2. The second tells how much total time the task takes to be completed
  3. The third one is supposed to give me the end date and time of the task when it is completed, knowing all of our assumptions.

So I am trying to build this formula where I could calculate the 3rd column.

Does anybody have an idea ? I tried to look in the forum and I was surprised that this question had never been raised

Thank you very much