user: Question: what is the date of vacancy when the position in table is 16th and the outgoing manager is Russell Slade?
Columns: ['Team', 'Outgoing manager', 'Manner of departure', 'Date of vacancy', 'Replaced by', 'Date of appointment', 'Position in table']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Milton Keynes Dons', 'Paul Ince', 'Signed by Blackburn Rovers (mutual consent)', '22 June 2008', 'Roberto Di Matteo', '2 July 2008', 'Pre-season']
SQL:

assistant: SELECT "Date of vacancy" FROM "Table" WHERE "Position in table" = '16th' AND "Outgoing manager" = 'Russell Slade';