Answer
$\color{blue}{36xy^2z^4\sqrt{5xy}}$
Work Step by Step
Factor the radicand so that at least one factor is a perfect square:
$=\sqrt{(1296x^2y^4z^{8})(5xy)}
\\=\sqrt{(36xy^2z^4)^2(5xy)}$
Bring out the square root of the perfect square factor to obtain:
$=\color{blue}{36xy^2z^4\sqrt{5xy}}$