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Here is the problem: A number plus 7 is 15. What is the number?

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Let x be the number: “a number plus 7” becomes x plus 7.

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Read the problem. Let x be the unknown number. “a number plus 7 is 15” translates to x plus 7 equals 15.

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Solve the linear equation. 1x plus 7 equals 15 → x equals (15 minus 7) / 1 equals 8.

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So the answer is The number is 8.

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Let x be the number: “a number plus 7” becomes x plus 7.

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Substitute x equals 8: (8) plus 7 equals 15, which checks out.