Intermediate Algebra (6th Edition)

$4^{8}y^{6}x^{2}$
$(\frac{4^{-4}}{y^{3}x})^{-2}$ [ Using $\frac{1}{a^{n}}= a^{-n}]$ $= (4^{-4}y^{-3}x^{-1})^{-2}$ $= (4^{-4})^{-2}(y^{-3})^{-2}(x^{-1})^{-2}$ [Using $(a^{m})^{n} =a^{m \times n} ]$ $=4^{8}y^{6}x^{2}$