CREATE TABLE table_18700 ("District" TEXT, "Incumbent" TEXT, "Party" TEXT, "First elected" FLOAT, "Result" TEXT, "Candidates" TEXT)

When was incumbent William B. Oliver first elected?
SELECT MAX("First elected") FROM table_18700 WHERE "Incumbent" = 'William B. Oliver'
SELECT MAX("First elected") FROM "table_18700" WHERE "Incumbent" = 'William B. Oliver'