Call the digits of the number to look for is a, b, cBecause of the need to find divisible by 18, the number that is divisible by 9SoFrom (1) and (2) we have:Infer:Because of the need to find 18 divisible, so moderate that number divisible by 9 2 medium, implying the unit digit is even.So no need to look for are:then (1) takes the form:A similar proof, we have:
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