user: ### NOW ANSWER:
Question: When is it that successor's formal installation has a Vacator of Ross Bass (D)?
Columns: ['State (class)', 'Vacator', 'Reason for change', 'Successor', "Date of successor's formal installation"]
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['South Carolina (3)', 'Olin D. Johnston (D)', 'Died April 18, 1965', 'Donald S. Russell (D)', 'April 22, 1965']
SQL:

assistant: SELECT "Date of successor's formal installation" FROM "Table" WHERE "Vacator" = 'Ross Bass (D)';