$\"\"$

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The sentence is “twice the sum of s and t decreased by s”.

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The word “sum” represents the symbol +.

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The word “decreased” represents the symbol $\"\"$ .

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$\"\"$

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The algebraic expression is $\"\"$

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$\"\"$

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

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

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$\"\"$ (Apply commutative property of addition: $\"\"$ )

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$\"\"$

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$\"\"$ (Apply associative property of addition: $\"\"$ )

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

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

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$\"\"$

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The simplified expression is $\"\"$ .