user: Question: How many vacancies happened on 25 May?
Columns: ['Team', 'Outgoing manager', 'Manner of departure', 'Date of vacancy', 'Replaced by', 'Date of appointment']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Albion Rovers', 'John McCormack', 'Resigned', '28 June', 'Paul Martin', '9 July']
SQL:

assistant: SELECT COUNT("Manner of departure") FROM "Table" WHERE "Date of vacancy" = '25 May';