#9z^8*8y^9#
(The exponent #2# in #(3z^4)^2# applies to everything inside the parenthesis. This means #3^2*(z^4)^2#, which equals #9*z^8#. When you have a exponent to an exponent, that means you have to multiply them together. If you apply this concept to #(2y^3)^3# too, then you will get #8y^9#).