user: Question: Name the state class for  Iowa admitted to the Union December 28, 1846
Columns: ['State (class)', 'Vacator', 'Reason for change', 'Successor', 'Date of successors formal installation']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['Virginia (1)', 'Vacant', 'Failure to elect', 'Isaac S. Pennybacker ( D )', 'Elected December 3, 1845']
SQL:

assistant: SELECT "State (class)" FROM "Table" WHERE "Reason for change" = 'Iowa admitted to the Union December 28, 1846';