Passing Parameter to Formula

I've got a parameter field where the user can input a number and I'd like a formula field to pick up this value and add it to another value it pulls from the database.

But I am not sure how the pass this value along.  For example, if the user inputs 10 for the IncentiveQty parameter value, I would like to have this value added to the value pulled from the Projections field.

How would I pass along this value and have it appended?

Thanks,