$\"\"$ $\"\"$ $\"\"$

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The equation is $\"\"$ .

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According to subtraction property of equality: Subtract 40 from each side.

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$\"\"$

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

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

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

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According to division property of equality: Divide each side by 2.

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$\"\"$

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$\"\"$ (Cancel common terms)

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

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

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

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Compare the values, the equation is true. $\"\"$

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The value of $\"\"$ .