Answer
$\sqrt{35}+\sqrt{21}$
Work Step by Step
Using the Distributive Property and the properties of radicals, then,
\begin{array}{l}
\sqrt{7}\left( \sqrt{5}+\sqrt{3} \right)
\\=
\sqrt{7(5)}+\sqrt{7(3)}
\\=
\sqrt{35}+\sqrt{21}
.\end{array}