Chapter 5 - Section 5.4 - Multiplying Polynomials - Exercise Set - Page 289: 18

$8x^3-2x^2-31x-20$

Using the Distributive Property, the given expression simplifies to \begin{align*} & [2x^2(4x)+2x^2(5)]+[-3x(4x)-3x(5)]+[-4(4x)-4(5)] \\\\&= [8x^3+10x^2]+[-12x^2-15x]+[-16x-20] \\\\&= 8x^3+(10x^2-12x^2)+(-15x-16x)-20 \\\\&= 8x^3-2x^2-31x-20 .\end{align*}