Answer
$-12b\sqrt b$
Work Step by Step
$-2\sqrt{3b^2}\times\sqrt{12b}\longrightarrow$ factor the radicands
=$-2\sqrt{b^2\times3}\times\sqrt{3\times4\times b}\longrightarrow$ multiplication property of square roots
=$-2\times\sqrt {b^2} \times(\sqrt 3\times\sqrt3)\times\sqrt4\times\sqrt b\longrightarrow$ simplify
=$-2\times b\times 3\times2\times\sqrt b\longrightarrow$ simplify
=$-12b\sqrt b$
