Get rid of the parentheses in the expression z - [3 - (x - y)].
First way? Work from the inside out:
z - [3 - x + y] = z - 3 + x - y.
Second way. Work from the outside in:
z - 3 + (x - y) = z - 3 + x - y.
Third way. Okay, we were joshin' you about the fire thing. Parentheses don't scare that easily.