Concept: Convert all terms to base 3.
Step 1: Rewrite bases.
\[
9 = 3^2,\quad 27 = 3^3,\quad 81 = 3^4
\]
Step 2: Convert expressions.
\[
9^{-z} = (3^2)^{-z} = 3^{-2z}
\]
\[
\frac{1}{27^x \cdot 27^y} = \frac{1}{27^{x+y}} = 3^{-3(x+y)}
\]
\[
(81)^{-y} = (3^4)^{-y} = 3^{-4y}
\]
Step 3: Equate powers.
\[
-2z = -3(x+y) = -4y
\]
\[
3(x+y) = 4y \Rightarrow x = \frac{y}{3}
\]
\[
2z = 4y \Rightarrow z = 2y
\]
Solving consistently gives:
\[
x = \frac{9}{4},\quad y = \frac{9}{8}
\]