CREATE TABLE table_18771 ("Serial & Branch" FLOAT, "Seaman" TEXT, "Mechanical" TEXT, "Secretariat" TEXT, "Supply" TEXT, "Electrical" TEXT, "Radio Electrical" TEXT, "Regulating" TEXT, "Medical" TEXT)

How many serial branches have radio electrial = rea-iv?
SELECT COUNT("Serial & Branch") FROM table_18771 WHERE "Radio Electrical" = 'REA-IV'
SELECT COUNT("Serial & Branch") FROM "table_18771" WHERE "Radio Electrical" = 'REA-IV'