Ratio

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Both watch faces are circular with radius 2cm. The materials used to make both watch faces have the same thickness. A is made entirely of plastic. B has a 20° sector of metal and a 340° sector of plastic. The ratio of the cost per cm² of the metal to the cost per cm² of the plastic is 3:2 Work out the ratio of the cost of the materials for A to the cost of the materials for B. Give your answer in its simplest form.