You can arrange them in 4! = 24 ways as follows:
(6, 7, 8, 9), (6, 7, 9, 8), (6, 8, 7, 9), (6, 8, 9, 7), (6, 9, 7, 8), (6, 9, 8, 7), (7, 6, 8, 9), (7, 6, 9, 8), (7, 8, 6, 9), (7, 8, 9, 6), (7, 9, 6, 8), (7, 9, 8, 6), (8, 6, 7, 9), (8, 6, 9, 7), (8, 7, 6, 9), (8, 7, 9, 6), (8, 9, 6, 7), (8, 9, 7, 6), (9, 6, 7, 8), (9, 6, 8, 7), (9, 7, 6, 8), (9, 7, 8, 6), (9, 8, 6, 7), (9, 8, 7, 6), Total = 24