user: Question: How many reasons for change were listed when Edward Hempstead was the successor?
Columns: ['District', 'Vacator', 'Reason for change', 'Successor', 'Date successor seated']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['Massachusetts 4th', 'Joseph B. Varnum (DR)', 'Resigned June 29, 1811 to become U.S. Senator', 'William M. Richardson (DR)', 'Seated November 4, 1811']
SQL:

assistant: SELECT COUNT("Reason for change") FROM "Table" WHERE "Successor" = 'Edward Hempstead';