The value of the expression $3^2 \sqrt{25} + 3 - \sqrt{81}$ is 39.

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Here are some related questions to expand your understanding:

1. What are the steps to simplify $3^2 \sqrt{25}$?
2. Why do we use the positive root when simplifying square roots like $\sqrt{25}$ or $\sqrt{81}$?
3. How does the order of operations apply in this expression?
4. Can square roots of negative numbers be evaluated similarly?
5. What happens if we use negative square roots instead?

Tip: When working with square roots, always consider whether the context specifies using the positive or negative root.