To simplify a fourth root, factor out all 4th powers because the 4th root of a positive quantity, A, raised to the fourth power simplifies to A. Recall that the fourth root is equivalent to 1/4 power.
(192x6y9)1/4 = [(16)(12)x4x2y4y4y]1/4
= 2xy2(12x2y)1/4 (Assuming x, y > 0)