$\"\"$

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Observe the figure, the shaded regions are rectangle figure and triangle figure.

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The base of the triangle is $\"\"$ and its height is $\"\"$ .

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The area of the triangle is $\"\"$ .

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$\"\"$

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$\"\"$

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Apply distributive property: $\"\"$ .

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$\"\"$

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$\"\"$ . $\"\"$

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The length of the rectangle is $\"\"$ and its width is $\"\"$ .

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The area of the rectangle is $\"\"$ .

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$\"\"$

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Apply distributive property: $\"\"$ .

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$\"\"$

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$\"\"$ . $\"\"$

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The area of shaded region is $\"\"$ .

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$\"\"$

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Combine like terms.

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$\"\"$

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$\"\"$ . $\"\"$

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The area of shaded region is $\"\"$ .