Number fields with an equation

I’m trying to allow the user to add to a total number on my app. I have 3 fields (2 numbers and one equation).

The user can input any number in “Number Referrals” and the Equation field totals the values of “Number Referrals and Total Amount of Referrals”. How do I make it so “Number Referrals” resets to 0 or is blank. Now it still shows the value that was last used. Also, if I first submit 5 and then 1, the equation field still adds 5 until I submit the form twice. Is there a way to fix that?