CREATE TABLE table_18438 ("District" TEXT, "Incumbent" TEXT, "Party" TEXT, "First elected" FLOAT, "Result" TEXT, "Candidates" TEXT)

When was James William Trimble first elected in the Arkansas 3 district?
SELECT MIN("First elected") FROM table_18438 WHERE "District" = 'Arkansas 3'
SELECT MIN("First elected") FROM "table_18438" WHERE "District" = 'Arkansas 3'