Simplify 9 square root of 2*3 square root of y

$9 \sqrt{2} \cdot 3 \sqrt{y}$

Multiply $9 \sqrt{2} (3 \sqrt{y})$ .

Multiply $3$ by $9$ .

$27 \sqrt{2} \sqrt{y}$

Combine using the product rule for radicals.

$27 \sqrt{y \cdot 2}$

Reorder factors in $27 \sqrt{y \cdot 2}$ .

$27 \sqrt{2 y}$