Please explain how the following MRP table is filled - the answers are given - just need to understand how its done

Example Problem - Solution A LT: 1 week B LT: 2 weeks LT: 1 week Using the product tree and lead times shown, complete the following table to determine the planned order receipts and releases. There are 50 as required in week 5 and 100 in week 6. D LT: 1 week E LT: 1 week Week Part Number 1 2 3 4 5 6 50 100 50 100 50 100 B 50 100 100 Planned Order Receipt Planned Order Release Planned Order Receipt Planned Order Release Planned Order Receipt Planned Order Release Planned Order Receipt Planned Order Release Planned Order Receipt Planned Order Release 50 100 50 50 100 D 50 100 100 E 50 100 50