#### Answer

$-1$

#### Work Step by Step

Using the product of the sum and difference of like terms which is given by $(a+b)(a-b)=a^2-b^2,$ the given expression is equivalent to
\begin{array}{l}\require{cancel}
(3+\sqrt{10})(3-\sqrt{10})
\\\\=
(3)^2-(\sqrt{10})^2
\\\\=
9-10
\\\\=
-1
.\end{array}