In Accounting for Decision Making and Control (9th ed) by Zimmerman (https://www.chegg.com/homework-help/Accounting-for-Decision-Making-and-Control-9th-edition-chapter-5-problem-21P-solution-9781259564550), in Chapter 5, problem 21 question F, I looked at the correct answer, but cannot understand how the answer is right. The original question in the book asks "What transfer price should Flat Images set to maximize firmwide profits? (Give a quantitative number.)"

My question is: Why are the manufacturing costs not deducted in the table (in addition to the marketing costs)?

How did one arrive at the answer of $800 being the ideal transfer fee?