7) Counting Password without repeating characters- Each character in a password is either a digit [0-9] or lowercase letter [a-z] or special characters [*, &, $, #]. How many valid passwords are there with the given restriction(s)?

a) Length 6. Characters can be special characters, digits, or letters, with no repetitions

b) Length 6. Characters can be special characters, digits, or letters, with no repetitions. The first character cannot be a special character.