Chapter 5 - Exponents and Polynomials - 5.2 - Multiplying Monomials - Problem Set 5.2 - Page 201: 65

$4x^3-3x^2-14x$

Using $a(b+c)=ab+ac$, or the Distributive Property, and then combining like terms, the given expression, $ 2x(x^2-3x-4)+x(2x^2+3x-6) ,$ simplifies to \begin{array}{l}\require{cancel} 2x^3-6x^2-8x+2x^3+3x^2-6x \\\\= (2x^3+2x^3)+(-6x^2+3x^2)+(-8x-6x) \\\\= 4x^3-3x^2-14x .\end{array}