user: Question: What are the years employed shown for Mathematics & Prefect Master?
Columns: ['Name', 'Employed', 'Position held', 'Honour', 'Citation']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['Davis, Phillip Harris (Phil)', '1951–2000', 'Mathematics & Prefect Master', 'Medal of the Order of Australia', "It's an Honour"]
SQL:

assistant: SELECT "Employed" FROM "Table" WHERE "Position held" = 'Mathematics & Prefect Master';