Linking dynamic value in formula

Hello all,

I'm having a little trouble doing what seems to be simple algebra.

Currently I have a total number of units, and some activities to reduce the number of units that come through. The activities aren't necessarily in any order, but what I'm looking to do, is to allow volume to adjust based on the components of all 3.

Example, right now my addressable units is 2000, but what I am looking for is for the volume to be dependent on the other reductions. So that when I reduce Volume by 5% using Exercise 1, Exercises 2 and 3 would be based off of the reduced volume of number 1, and vice versa for all 3.

Then ultimately, I would apply a cost per unit to that to realize a cost savings figure.

Thank you!