Well, forst you have to do the opposite to find what y equals. You have to start on the side with the variable. The opposite off adding is subtaction.
-y+56=167
-56.
-y+56=167
-56
What you do to one side you must do to the other, you mark out 56 and take 167-56.
That equals 111.
111=y
I hope this explains why! :)