please help this question with permutation and combination

1. Suppose English letters {A, B, C, D, E, F, G, H, I, J, K, L} are available now

And the numbers {1, 2, 3, 4} form a six-digit password.

How many different passwords can be formed in the following situations:

(a) English letters and numbers cannot be repeated; (2 points)

(b) English letters and numbers can be repeated. (2 minutes)