`4x^3 y (-2x^2y^3)(-xy^3)`
`=[4.(-2).(-1)].(x^3 .x^2 .x).(y.y^3 .y^3)`
`=8x^6y^7`
\(4x^3y\left(-2x^2y^3\right)\left(-xy^3\right)\)
\(=\left[4\cdot\left(-2\right)\right]\left[x^3\cdot x^2\cdot\left(-x\right)\right]\left(y\cdot y^3\cdot y^3\right)\)
\(=\left(-8\right)\left(-x\right)^6\left(y\right)^7\)
\(=-8x^6y^7\)
\(4x^3y\left(-2x^2y^3\right)\left(-xy^3\right)=8x^6y^7\)