Create a Variable in a table column from a drop down list

To add to original post here's the table.

What I'm trying to do is make Precentage column a drop down so user can select 2 thru 8, but only one value. The requirement is that every line is a independant percentage of the other lines. As you see it now there is multi lines but with different precentage. That because I joined it to a second table with Squence as the key and the precentages of 2 thur 8. But that is not working like I had hoped. I'm thinking since the 2 thru 8 in constant there should be a way to set them as a fix value some how.

Then take the users selected precentage into a calculation for the field not shown "Future Cost". 

From a spreadsheet view, it's the fields in RED that I'm trying to come up with in my report.

Thanks!!