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13. Now assume that the Stitching Division has the option of buying buttons from an external supplier for $4.50 per button. Everything else remains the same as above, i.e., the Buttons Division can still sell to an external buyer for $5 per button, and revenues and costs per unit stay the same as in the table above. (a) If the Stitching Division buys buttons from the Buttons Division, will the operating income of Forever Inc. increase or decrease, and by how much? (b) What is Stitching Division/Buttons Division operating income if the Stitching division does not buy the buttons from the Buttons division