user: Question: Name the transfer fee with a transfer window of Summer for Schollen
Columns: ['Name', 'Country', 'Type', 'Moving from', 'Transfer window', 'Transfer fee']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Bruzzese', 'BEL', 'Transferred', 'RFC Liège', 'Summer', 'Undisclosed']
SQL:

assistant: SELECT "Transfer fee" FROM "Table" WHERE "Transfer window" = 'Summer' AND "Name" = 'Schollen';