CREATE TABLE table_18680 ("District" TEXT, "Incumbent" TEXT, "Party" TEXT, "First elected" FLOAT, "Result" TEXT, "Candidates" TEXT)

How many districts does william b. oliver represent?
SELECT COUNT("District") FROM table_18680 WHERE "Incumbent" = 'William B. Oliver'
SELECT COUNT("District") FROM "table_18680" WHERE "Incumbent" = 'William B. Oliver'