I'm not 100% sure of what you are looking for, but Tableau is an 'additive' product so if you combine 3116 and 3367 it should come to 18 unless you do some magic like change the figure to an average.
If you group 3116 and 3367 you can then edit the alias of the combined product to anything you like, so could rename that to Doc count 2 or something like that - is this what you are after ?
From what I understand of your question it sounds like you're going to want to use a(n) LoD calculation. These can be very powerful in crafting visualizations and analysis, especially when you start to understand the syntax involved.
I'm by no means an expert but I will direct you to one of my favorite resources, Top 15 Tableau LOD Expressions (Practical Examples)
If you look at their first example you'll notice that it's pretty close to your question. See if following those steps with "No. of Inquiries" replacing "Number of Orders" and "Doc No." replacing "Customer ID" and let us know if that solves it. Good luck!
Thank you for your prompt response. The Doc. No. is a description with a string data type in this instance and not an actual number. I am trying to get a count of how many documents had a particular volume of inquiries. Each document is unique. I should have used a clearer dimension name for the document.