CREATE TABLE table_12738 ("Year" FLOAT, "Competition Description" TEXT, "Location" TEXT, "Apparatus" TEXT, "Rank-Final" FLOAT)

What is Apparatus, when Rank-Final is greater than 6, and when Competition Description is 'U.S. Championships'?
SELECT "Apparatus" FROM table_12738 WHERE "Rank-Final" > '6' AND "Competition Description" = 'u.s. championships'
SELECT "Apparatus" FROM "table_12738" WHERE "Competition Description" = 'u.s. championships' AND "Rank-Final" > '6'