$\"\"$

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The given values are $\"\"$ .

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The nth term of the arithmetic series $\"\"$ ,

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Where $\"\"$ is the first term and $\"\"$ is the nth term.

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

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Distribute terms using distributive property: $\"\"$ .

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$\"\"$

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$\"\"$ (Product of two same signs is positive)

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$\"\"$ (Add: 91 + 4 = 95) $\"\"$

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Apply subtraction property of equality: a = b then $\"\"$ .

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$\"\"$ (Subtract 95 from each side)

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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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Apply division property of equality: a = b then $\"\"$ .

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$\"\"$ (Divide each side by negative 4)

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$\"\"$ (Cancel common terms)

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

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The sum of an arithmetic series $\"\"$ .

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Where $\"\"$ is the first term and $\"\"$ is the nth term.

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

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$\"\"$ (Add: 91 + 15 = 106)

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

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

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The value of $\"\"$ .