user: Question: what is the date of vacancy when the team is Firpo and replaced by is Oscar Benitez?
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: ['Nejapa', 'Mauricio Cienfuegos', 'Mutual consent', '14 August 2008', 'Daniel Uberti', '5 September 2008', '10th']
SQL:

assistant: SELECT "Date of vacancy" FROM "Table" WHERE "Team" = 'Firpo' AND "Replaced by" = 'Oscar Benitez';