CREATE TABLE table_728 ("District" TEXT, "Incumbent" TEXT, "Party" TEXT, "First elected" FLOAT, "Result" TEXT, "Candidates" TEXT)

What's the year of the first election of the district whose incumbent is Edwin E. Willis?
SELECT "First elected" FROM table_728 WHERE "Incumbent" = 'Edwin E. Willis'
SELECT "First elected" FROM "table_728" WHERE "Incumbent" = 'Edwin E. Willis'