\"\"

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The proportion is \"\"

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\"\"             (Means–Extremes Property of Proportion: \"\" then ad = bc)

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\"\"               (Multiply: \"\")

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\"\"

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\"\"           (Divide each side by 15)

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 \"\"                   (Cancel common terms)

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a = 9                           (Divide: \"\")\"\"

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The value of a is 9.