Answer
-18y$\sqrt (3y)$
Work Step by Step
-2 * $\sqrt (81 * 3 * y^{2} * y)$
Step 1: Split Numbers Into Perfect Squares
-2 * $\sqrt (9^{2} * 9 * 3 * y^{2} * y)$
Explanation: 81 = 9 * 9 * 9 = $9^{2}$ * 9
Step 2: Remove all perfect squared numbers/variables and put them on the outside
-2(9)(y) * $\sqrt (3y)$
Step 3: Simplify
-18y$\sqrt (3y)$