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