How many ways can I arrange or rearrange The letters A B C D E F?

The letters A, B, C, D, E, and F can be arranged in 6! (6 factorial) ways. This calculation equals 720, as 6! = 6 × 5 × 4 × 3 × 2 × 1 = 720. Therefore, there are 720 different ways to arrange or rearrange the letters.