Answer
$-99+\sqrt 7$
Work Step by Step
$(3+5\sqrt 7)(2-3\sqrt 7)$
=$3(2-3\sqrt 7)+5\sqrt 7(2-3\sqrt 7)$
=$6-9\sqrt 7+10\sqrt 7-3\sqrt 7(5\sqrt 7)$
=$6+(-9+10)\sqrt 7-(3\times5)(\sqrt 7\times\sqrt 7)$
=$6+1\sqrt 7-15(7)$
=$6+\sqrt 7-105$
=$6-105+\sqrt 7$
=$-99+\sqrt 7$
