(2y+z)-(z-2y)=2у+z-z+2y=4y
(x+3)-(5x-7)=x+3-5x+7=10-4x
(2a-1)+(3-4a)=2a-1+3-4a=2-2a
(a+b)-(a-b)-(b-a)=a+b-a+b-b+a=b+a
3m-(2m-3)+(2-m)=3m-2m+3+2-m=5
(3y-1)-(2y-2)+(y-3)=3y-1-2y+2+y-3=2y-2