Simplify the expression $\left( \displaystyle \frac{x^2 y^4 z^2 x^{-5}}{x^5 y^4 z^2 y^4}\right)^{-3}$ into the form $x^r y^s z^t$ and identify $r, s$ and $t$.

$r$	=
$s$	=
$t$	=