5.$=-5xy^3z.16x^4=(-5.16)(x.x^4).y^3z=-80x^5y^3z$
6. $=4x^4y^6.(-2)xy=(-2.4)(x^4.x)(y^6.y)=-8x^5y^7$
7. $=\frac{-2}{3}xy^2z.9x^4y^2=(\frac{-2}{3}.9)(x.x^4)(y^2.y^2)z=-6x^5y^4z$
8. $=-2xy^3.\frac{3}{8}.x^2z^4=(-2.\frac{3}{8}).(x.x^2)y^3z^4=\frac{-3}{4}x^3y^3z^4$
9. $=\frac{1}{4}x^4y^6.(-2)xy=\frac{1}{4}(-2).(x^4.x)(y^6.y)=\frac{-1}{2}x^5y^7$