how do you ''switch out'' the answer in a problem like 54-n=36

Question

54-n=36.    54-36=18     36-36=0.     

18-n=0

Now how do you get that to switch to say n=18 instead of 0

Answer 1

54-n=36

54-n+n=36+n

54+0=36+n

54-36=36+n-36

54-36=n+36-36

54-36=n+0

18=n