CREATE TABLE table_18338 ("District" TEXT, "Incumbent" TEXT, "Party" TEXT, "First elected" FLOAT, "Result" TEXT, "Candidates" TEXT)

who is the incumbent where the candidates is william v. chappell, jr. (d) unopposed?
SELECT "Incumbent" FROM table_18338 WHERE "Candidates" = 'William V. Chappell, Jr. (D) Unopposed'
SELECT "Incumbent" FROM "table_18338" WHERE "Candidates" = 'William V. Chappell, Jr. (D) Unopposed'