(2.9x-0.5y)+(2.9x+1.5y)
(4x-8y)-(5x-18y)
(3x+y)-(x-4y)
(x+6y)-(8x-7)

(2,9x-0,5y)+(2,9 +1,5y)=2,9x-0,5y+2,9+1,5y=2,9x+y+2,9(4x-8y)-(5x-18y)=4x-8y-5x+18y=-x+10y(3x+y)-(x-4y)=3x+y-x+4y=2x+5y(x+6y)-(8x-7)=x+6y-8x+7=-7x+6y+7