How to use Equal addition

 
This is how you use equal addition.
You had 39 fans and 19 went away so what you do is, We plus one to the
19 to get a clean number 20 then we plus one to the 39 to make 40.Finally we do 40 -20=20 and 0-0=0.And your answer is 20.That is how you do equal addition.