Below is an instruction that describes a task. Write a response that appropriately completes the request.

### Instruction:
List the number of vacators when successors were formally installed on June 22, 1868.

### Inputs:
table_name: table, columns: ['State (class)', 'Vacator', 'Reason for change', 'Successor', 'Date of successors formal installation']

### Response:
SELECT COUNT Vacator FROM table WHERE Date of successors formal installation = June 22, 1868