Unable to solve roots expression

Expression 1:$\displaystyle \frac{1}{\sqrt[5]{8xy^2}}$

My Work:

$\displaystyle \frac{1}{\sqrt[5]{8xy^2}}=\frac{1}{\sqrt[5]{8xy^2}}*\frac{\sqrt[5]{8^4x^4y^3}}{\sqrt[5]{ 8^4x^4y^3}}=\frac{4\sqrt4}{8xy}$

The only answer choices I have for this self test are

Answer: $\displaystyle (8xy^2)^{-1/5}$

Expression 2:

$\displaystyle \frac{y^3}{\sqrt[4]y}$

The author states the correct answer for expression 2 is $\displaystyle x^{11/4}$, and yes they say "x" not "y"....either way not sure how to arrive at this answer either.

This is a self teaching algebra book, however the author decided to not show her work in any of the chapter reviews which is frustrating.

Thanks again!