a) -2a+2+8a-3a=-2a+8a-3a+2=3a+2
b) x+2y-6x-5y-2y=x-6x+2y-5y-2y=-5x-5y
c) 2x²-3y+5x+2y-x²=2x²-x²+5x-3y+2y=x²+5x-y