$\"\"$

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The equation is $\"\"$ .

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$\"\"$ (Add 81 to each side) \ \

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$\"\"$ (Apply additive inverse property: $\"\"$ ) \ \

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$\"\"$ (Apply additive identity property: $\"\"$ )

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$\"\"$ (Apply additive inverse property: $\"\"$ ) $\"\"$

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$\"\"$ (Divide each side by 9)

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$\"\"$ (Cancel common terms)

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$\"\"$

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$\"\"$

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$\"\"$ (Evalute powers: $\"\"$ )

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$\"\"$ (Apply squareroot each side)

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$\"\"$ (Cancel roots and squares) $\"\"$

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The value of $\"\"$ is $\"\"$ .