If you want to learn about Point of Total Assumption (PTA) concept and formulas, how the formulas are derived, read the full 5-part series on PTA on the Deep Fried Brain Project blog:
Point of Total Assumption (PTA) in FPIF Contracts (5-part series)
Download PDF Attachment
To download the file for Seller Fee Calculation problem, click the following link:
Seller Fee Calculation and PTA in FPIF Contracts (Download PDF)