CREATE TABLE table_10421 ("Team" TEXT, "Established" FLOAT, "Big Ten Conference Titles" FLOAT, "National Titles" FLOAT, "Venue" TEXT, "Opened" FLOAT, "Capacity" FLOAT)

When is the earliest year opened for huff hall that was established after 1974?
SELECT MIN("Opened") FROM table_10421 WHERE "Venue" = 'huff hall' AND "Established" > '1974'
SELECT MIN("Opened") FROM "table_10421" WHERE "Established" > '1974' AND "Venue" = 'huff hall'