The Charlotte plant receives some products used in the manufacturing of envelopes, cups and packaging from the South Carolina plant. Recently there have been some heated discussions about the prices charged Charlotte by the South Carolina plant. The product, cremodium, has cost Charlotte $80 per batch. This covers all marginal costs incurred by the South Carolina facility. The South Carolina facility is a profit center and agues that they can sell cremodium on the open market for $120. Which method, as presented in your text, should be used in this instance and why? Does it make a difference if the South Carolina plant has no idle capacity?