Figuring out Availability based upon work/task schedule

Ok, here's what I'm trying to accomplish.

I have a task (task 3 for argument's sake) at work that is non assigned. I am trying to gauge how people are performing on the task (are there those who do it more than others).

What I am wanting to accomplish is to figure out a ratio of how many people were available to accomplish Task 3, by excluding people who are performing Tasks 1 or 2, not working the same shift as when the task was available, or not working on that day.

I have all the available data: Schedules for tasks 1 and 2 and results of task 3 (who did it, and when it came in).

I'm just looking for ideas on where to go next.

See the example for the data.