Chapter 4 - Polynomials - 4.5 Multiplication of Polynomials - 4.5 Exercise Set - Page 269: 41

$t^2+4t-21$

Using $(a+b)(c+d)=ac+ad+bc+bd$ or the product of $2$ binomials, the given expression, $ (t+7)(t-3) $, is equivalent to \begin{array}{l}\require{cancel} t(t)+t(-3)+7(t)+7(-3) \\\\= t^2-3t+7t-21 \\\\= t^2+4t-21 .\end{array}