CREATE TABLE table_63806 ("Rank" FLOAT, "Rowers" TEXT, "Country" TEXT, "Time" TEXT, "Notes" TEXT)

What is the highest rank with the notes of sa/b, and a time of 6:39.07?
SELECT MAX("Rank") FROM table_63806 WHERE "Notes" = 'sa/b' AND "Time" = '6:39.07'
SELECT MAX("Rank") FROM "table_63806" WHERE "Notes" = 'sa/b' AND "Time" = '6:39.07'