CREATE TABLE table_18345 ("District" TEXT, "Incumbent" TEXT, "Party" TEXT, "First elected" FLOAT, "Result" TEXT, "Candidates" TEXT)

What year was Otto Passman (d) unopposed first elected?
SELECT MAX("First elected") FROM table_18345 WHERE "Candidates" = 'Otto Passman (D) Unopposed'
SELECT MAX("First elected") FROM "table_18345" WHERE "Candidates" = 'Otto Passman (D) Unopposed'