Chapter 5 - Exponents and Polynomials - 5.3 - Multiplying Polynomials - Problem Set 5.3 - Page 207: 22

$21x^2-25x-4$

Using the Distributive Property and then combining similar terms, the given expression, $ (3x-4)(7x+1) ,$ is equivalent to \begin{array}{l}\require{cancel} 3x(7x)+3x(1)-4(7x)-4(1) \\\\= 21x^2+3x-28x-4 \\\\= 21x^2-25x-4 .\end{array}