Answer
$-83+3\sqrt{35}$.
Work Step by Step
The given expression is
$=(\sqrt{7}-3\sqrt{5})(\sqrt{7}+6\sqrt{5})$
Use the FOIL method.
$=\sqrt{7}\cdot\sqrt{7}+6\sqrt{7}\cdot \sqrt{5}-3\sqrt5\cdot \sqrt{7}-18\sqrt5\cdot\sqrt{5}$
Use product rule.
$=(\sqrt{7})^2+6\sqrt{35}-3\sqrt{35}-18(\sqrt5)^2$
Simplify.
$=7+3\sqrt{35}-90$
$=-83+3\sqrt{35}$.
