Subtracting a Formula

[DaniQ]

Dilemma:

I need to subtract one column (drop down box) from another column (drop down box) to have a total and I cannot firure out how to work the formula?

I am using acrobat X pro

Competency Level	Management Competency Level	Self vs. Manager
2 - Trained	4- Advanced	2

Management Competency Level - Competency Level = Self vs. Manager (formula to be inserted here)

                    4 - Advanced             -        2 - Trained      =     2

Can anyone help me?