Chapter 5 - Exponents and Polynomials - 5.3 - Multiplying Polynomials - Problem Set 5.3 - Page 207: 13

$x^2+5x-24$

Using the Distributive Property and then combining similar terms, the given expression, $ (x+8)(x-3) ,$ is equivalent to \begin{array}{l}\require{cancel} x(x)+x(-3)+8(x)+8(-3) \\\\= x^2-3x+8x-24 \\\\= x^2+5x-24 .\end{array}