$\"\"$

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Perimeter of the rectangle is 40 units.

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Formula for perimeter of a rectangle is $\"\"$ , where l is length and w is width.

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$\"\"$ (Write the formula)

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

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Evaluate the expression inside the parentheses.

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

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

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

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$\"\"$ (Subtract 18 from each side)

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

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

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$\"\"$ (Divide each side by 2)

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$\"\"$ (Cancel common terms)

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

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The value of x is 11 units. $\"\"$

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The value of x is 11 units.