3xy*(3x²+2xy)=9x^3y+6xy²
-2x²*3xyz=-6x^3yz
9xyz*(xy+yz)=9x²y²z+9xy²z²
3xy*(-2xy²)=-6x²y^3
5ab*(3a²bc+bc²)=15a^3b²c+5ab²c²