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Define x :
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Let the number be x.
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Construct equation:
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Nine more than the product of 4 and the number is 73
⇒4x + 9 = 73
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Solve for x:
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4x + 9 = 73
4x = 73 -9
4x = 64
x = 16
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Answer: Ken's number is 16.
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