The expression $\left(\frac{2}{3}\right)^{-4}$ simplifies to $\frac{81}{16}$.

Would you like further details or have any other questions?

Here are some related questions to explore:

1. How do negative exponents affect fractions?
2. What is the general rule for simplifying $\left(\frac{a}{b}\right)^{-n}$?
3. How does the reciprocal work with negative powers?
4. Can this concept be extended to algebraic fractions?
5. What are some common mistakes when working with negative exponents?

Tip: Remember that a negative exponent flips the fraction before applying the exponentiation.