\"\"

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The equation is \"\".

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What number plus 3 equals to 12 ?      (Write the equation as a question)

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The question is C.

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The solution is 9.\"\"

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Check whether 9 is a solution.

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\"\"                      (Write the equation)

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\"\"                      (Substitute \"\")

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\"\"                          (Add: \"\")

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\"\" \"\" is the solution of the equation.\"\"

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\"\" \"\" is the solution of the equation.