CREATE TABLE table_764 ("District" TEXT, "Incumbent" TEXT, "Party" TEXT, "First elected" FLOAT, "Result" TEXT, "Candidates" TEXT)

When was the Tennessee 3 district incumbent first elected?
SELECT MAX("First elected") FROM table_764 WHERE "District" = 'Tennessee 3'
SELECT MAX("First elected") FROM "table_764" WHERE "District" = 'Tennessee 3'