$\"\"$

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The expression is $\"\"$ .

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$\"\"$ (Write the equation)

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$\"\"$ (Apply distributive property: $\"\"$ )

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$\"\"$ (Multiply: $\"\"$ )

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$\"\"$ (Subtract 21 from each side)

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$\"\"$ (Subtract: $\"\"$ ) $\"\"$

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

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

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$\"\"$ (Cancel common terms)

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$\"\"$ (Divide: $\"\"$ )

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The solution is $\"\"$ . $\"\"$

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Check:

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Substitute $\"\"$ in the equation.

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$\"\"$ (Write the equation)

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$\"\"$ (Substitute $\"\"$ )

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$\"\"$ (Multiply: $\"\"$ )

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$\"\"$ (Subtract: $\"\"$ )

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$\"\"$ (Multiply: $\"\"$ )

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The solution was checked. $\"\"$

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The solution is $\"\"$ .