X^2y+y*x*y=x^2y+y^2x
3x*6y^2-5x^2*7y=18y^2x-35x^2y
2a*a^2*3b+a*8c=6a^3b+8ac
8x*3y*(-5y)-7x^2*(-4y)=-120y^2x+28x^2y
11a^5-8a^5+3a^5+a^5=a^5(11-8+3+1)=7a^5
1,9x^3-2,9x^3-x^3=x^3(1,9-2,9-1)=-2x^3
20xy+5yx-17xy=xy(20+5-17)=8xy
8ab^2-3ab^2+ab^2-7ab^2=ab^2(8-3+1-7)=-ab^2.