CREATE TABLE table_18557 ("District" TEXT, "Incumbent" TEXT, "Party" TEXT, "First elected" FLOAT, "Result" TEXT, "Candidates" TEXT)

Which district has the incumbent Wilbur Mills and a re-elected result?
SELECT "District" FROM table_18557 WHERE "Result" = 'Re-elected' AND "Incumbent" = 'Wilbur Mills'
SELECT "District" FROM "table_18557" WHERE "Incumbent" = 'Wilbur Mills' AND "Result" = 'Re-elected'