The straightforward solution is to bind the result text box to a page variable. On page focus, set this variable to an empty string so there is no result shown yet. On the “Component tap” event for your button, simply do the calculation from all your input variables, and assign the result to the page variable (to which you bound the results text box).
But you said “I cannot assign the result to another variable so that I can tie the button to that 3rd variable” but I don’t understand why you don’t want to (or can’t do this).
So I tried it again. I did not know that there was duplicate steps that I had to do. Anyway, I want to do something simple formula before I apply it to a complex formula I am thinking about. Thank you for all your input. I was about to give up on it.