user: Question: Which Transfer fee has a Moving from of Youth system, and a Nat of MAR?
Columns: ['Nat.', 'Name', 'Moving from', 'Type', 'Transfer window', 'Ends', 'Transfer fee']
Types: ['text', 'text', 'text', 'text', 'text', 'real', 'text']
Sample row: ['NED', 'Engelaar', 'Twente', 'Transfer', 'Summer', 2011.0, '€ 6m']
SQL:

assistant: SELECT "Transfer fee" FROM "Table" WHERE "Moving from" = 'Youth system' AND "Nat." = 'MAR';