CREATE TABLE table_18629 ("District" TEXT, "Incumbent" TEXT, "Party" TEXT, "First elected" FLOAT, "Result" TEXT, "Candidates" TEXT)

What district is incumbent robert l. mouton from?
SELECT "District" FROM table_18629 WHERE "Incumbent" = 'Robert L. Mouton'
SELECT "District" FROM "table_18629" WHERE "Incumbent" = 'Robert L. Mouton'