You have to keep in mind that what you do to one side of the equation you have to do the same exact thing to the other side of the equation. It makes life easier if we join like terms
n - 4 = 3n - 6
we want to join the "n" terms right? so how can we move all the n's to one side of the equation?
n - n - 4 = 3n - n - 6
notice that I subtracted "n" on both sides of the equation
-4 = 2n - 6
now we need to move the constant numbers together and place them on the other side.
-4 + 6 = 2n - 6 + 6
notice I added 6 to both sides of the equation
2 = 2n
solve for n
n = 1