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$\"\"$

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The perimeter of a rectangle is $\"\"$ .

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$\"\"$ (Substitute 50 for P)

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

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$\"\"$

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

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$\"\"$ (Split the terms)

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$\"\"$ (Cancel common terms)

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

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$\"\"$ (Subtract each side by l)

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

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

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The polynomial expression is $\"\"$ .

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$\"\"$

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$\"\"$ (Multiply each side by l) \ \

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$\"\"$ (Substitute A for $\"\"$ since it is area of rectangle formula) \ \

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

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

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Area of a rectangular pen is $\"\"$ . $\"\"$

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Area of a rectangular pen is $\"\"$ .