$\"\"$

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The equation is $\"\"$ .

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Apply subtraction property of equality: Subtract 12 from each side.

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$\"\"$

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Apply commutative property of addition: a + b = b + a.

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$\"\"$

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

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

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Apply multiplication property of equality: Multiply each side by negative $\"\"$ .

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$\"\"$

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$\"\"$ (Cancel common terms)

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

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Apply subtraction property of equality: Subtract 15 from each side.

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$\"\"$

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

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

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Check:

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To check the solution, substitute $\"\"$ in original equation $\"\"$ .

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$\"\"$

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$\"\"$ (Add: $\"\"$ )

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

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

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The equality is true. $\"\"$

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The value of $\"\"$ .