Answer
$-\sqrt3$
Work Step by Step
$3\sqrt3-2\sqrt{12}\longrightarrow$ factor the perfect square out of 12
=$3\sqrt3-2\sqrt{4\times3}\longrightarrow$ multiplication property of square roots
=$3\sqrt3-2(\sqrt{4})(\sqrt3)\longrightarrow$ simplify
=$3\sqrt3-2(2)(\sqrt3)\longrightarrow$ multiply
=$3\sqrt3-4\sqrt3\longrightarrow$ use distributive property
=$\sqrt3(3-4)\longrightarrow$ simplify
=$-\sqrt3$
