CREATE TABLE table_24398 ("District" TEXT, "Vacator" TEXT, "Reason for change" TEXT, "Successor" TEXT, "Date successor seated" TEXT)

When william b. campbell (u) is the successor what is the district?
SELECT "District" FROM table_24398 WHERE "Successor" = 'William B. Campbell (U)'
SELECT "District" FROM "table_24398" WHERE "Successor" = 'William B. Campbell (U)'