Hi everyone! I have overthought this formula so much that I am completely stuck. This is the problem I'm trying to calculate. If you have any ideas, I would love to hear them.

Volunteers are recruited at .4 volunteers per month starting 1/1/2018.
They stay on with the company for 10 months and then roll off.
Recruitment ends 5/12/2019
The total project ends 3/10/2020 (and all volunteers should be gone at this time)
I need to determine how many volunteers will be with us monthly over the entire course of the project.

I will be graphing this data to present and I honestly have been working on it for hours and cannot manage to get the formula to be correct.