Notice that the elements of the X subset are integer even numbers.
Take z=-1 => 2z+2 = -2+2 = 0
Take z=0 => 2z+2 = 2
Take z = 1 => 2z+2 = 4
Notice that the elements of the Y subset are integer odd numbers.
Take z = -1 => 2z+1 = -1
Take z=0 => 2z+1 = 1
Take z = 1 => 2z+1 = 3
The union of X and Y subsets is a set containing the collection of all the elements of the X and Y subsets.
XUY = Z = W
Evaluating the difference XUY-W yields a set of elements that belong to XUY but they do not belong to W.
Since XUY = W => the result of difference is W or XUY.