Chapter 5 - Exponents and Polynomials - 5.3 - Multiplying Polynomials - Problem Set 5.3 - Page 207: 23

$x^3+7x^2+21x+27$

Using the Distributive Property and then combining similar terms, the given expression, $ (x+3)(x^2+4x+9) ,$ is equivalent to \begin{array}{l}\require{cancel} x(x^2)+x(4x)+x(9)+3(x^2)+3(4x)+3(9) \\\\= x^3+4x^2+9x+3x^2+12x+27 \\\\= x^3+(4x^2+3x^2)+(9x+12x)+27 \\\\= x^3+7x^2+21x+27 .\end{array}