Answer
$16xy\sqrt[3] {3y}$
Work Step by Step
$2\sqrt[3] {24x^3y^4}+4x\sqrt[3] {81y^4}$ Factor.
$2\sqrt[3] {8x^3y^3}\sqrt[3] {3y}+4x\sqrt[3] {27y^3}\sqrt[3] {3y}$ Simplify.
$4xy\sqrt[3] {3y}+12xy\sqrt[3] {3y}$ Combine like radicals.
$16xy\sqrt[3] {3y}$
