#### Answer

$-2$

#### Work Step by Step

$\bf{\text{Solution Outline:}}$
To simplify the given radical expression, $
(\sqrt{7}+3)(\sqrt{7}-3)
,$ use the special product on multiplying the sum and difference of like terms.
$\bf{\text{Solution Details:}}$
Using the product of the sum and difference of like terms which is given by $(a+b)(a-b)=a^2-b^2,$ the expression above is equivalent\begin{array}{l}\require{cancel}
(\sqrt{7})^2-(3)^2
\\\\=
7-9
\\\\=
-2
.\end{array}