$\"\"$

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The equation is $\"\"$ .

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Distribute terms using distributive property: $\"\"$ .

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$\"\"$

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$\"\"$

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$\"\"$

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Add 21 to each side.

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$\"\"$

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$\"\"$

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Divide each side by 12.

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$\"\"$

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$\"\"$

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$\"\"$

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The value of $\"\"$ .