2
a) 2x-5
b) 9(x+y)
c) (a+b+c)/3
3
a) (7a-b)-(4a-2b)=7a-b-4a+2b=3a+b
b) -(8x+3y)+(2x+5y)=-8x-3y+2x+5y=-6x+2y
