user: Question: How many serial branches have radio electrial = REA-IV?
Columns: ['Serial & Branch', 'Seaman', 'Mechanical', 'Secretariat', 'Supply', 'Electrical', 'Radio Electrical', 'Regulating', 'Medical']
Types: ['real', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: [1.0, 'OD ( Ordinary Seaman )', 'ME II', 'WTR II', 'SA II', 'EN II', 'REN II', 'PM II', 'MA II']
SQL:

assistant: SELECT COUNT("Serial & Branch") FROM "Table" WHERE "Radio Electrical" = 'REA-IV';