CREATE TABLE table_28643 ("Rank by average" FLOAT, "Place" FLOAT, "Couple" TEXT, "Total points" TEXT, "Number of dances" FLOAT, "Average" TEXT)

How many ranks by average when Keiron & Brianne are the couple?
SELECT COUNT("Rank by average") FROM table_28643 WHERE "Couple" = 'Keiron & Brianne'
SELECT COUNT("Rank by average") FROM "table_28643" WHERE "Couple" = 'Keiron & Brianne'