Can I use number of elapsed week as a parameter to dynamically change work?

Hi,

For a task like project management, we could assume that a project manager will work on it for 3 hours every week from the week the project starts until the week the project ends. So, if the project lasts for 4 weeks, it would be 12 hours of work; if the project lasts for 5 weeks, it would be 15 hours of work.

Is there a way that I can create a dynamically calculated amount of work as "work = number of weeks * 3h per week"?

What I have done, is

1. I assume each work day is equal to 6 hours of work to take into account that people are interrupted during their working days. So, I have set my project calendar to have working days Monday to Friday, with each day having hours from 09:00-12:00 and 13:00-16:00; and I have set the project parameters as "1d = 6h"
2. I have created a Project Start Date milestone task and a Project End Date milestone task, both at duration 0d.
3. I have created a task called "Project management" which is a "fixed duration - not effort driven" task.
4. Create three dummy tasks ("Task 1", "Task 2", "Task 3"). They are all "fixed work", each has work = 5 d (i.e., 30 h in my project).
5. Chain the three dummy tasks (i.e., Task 1 is a predecessor of Task 2, which is a predecessor of Task 3).
   1. Note that I do not chain the "Project management" task.
6. Assigned one resource ("Person A") to the three dummy tasks, each time at units 100%.
   1. As a result, each task gets a duration of "5d?", and the project start and end dates are now 15 days apart.
7. Turn "Project Management" into a banana task by
   1. copy the project start date from the milestone and paste it as a link in the "Project management" start date
   2. copy the project end date from the milestone and paste it as a link in the "Project management" end date
   3. As a result, this task's duration also becomes "15d?" (estimated)
8. Assign another person ("PM") to the Project Management task with resource units = 10%.
   1. As a result, the effort becomes 9 hours (15 days * 6 hours / day * 10%)

As a result of the banana task setting, the start and end dates for "Project management" will automatically adapt when the start or end dates of the Project change.

Now I adapt Task 1, Task 2, and Task 3 to having work = 10 days each. As a result, the project start and end dates are now changed to being 30 days apart. Since "Project management" has linked dates, its own duration also becomes 30 days. So far, so good.

The problem is that "work" for the "Project management" task stays fixed at 9 hours. I would like it to increase to 18 hours (6 weeks * 3 hours / week)

In other words, I want to model that the Project Management task will take 3 hours per week, each and every week for the entire project.

If the project lasts for a different number of weeks, I would like the work to change proportionally and automatically.

In Excel, I would insert a formula much like "work in hours = (week of the project end date - week of the project start date) * 3 hours"

How can I get MS Project to behave like this?