5*x3*y*(-4*x5*y3)

-6*х4*у3*(-3*х5*у6)

18а*2b3:27*а8b6

5x³y( -4x^5 y³)= - 20 x^8 y^4

-6 x^4 y³ ( -3 x^5 y^6)=18 x^9 y^9

18 a * 2b³ :27a^8 b^6=2/3 a^(-7)b^(-5)=2/(3a^7 b^5)