Suppose a password must have at least 9 but no more than 13 characters, where each character is a lowercase letter (a-z), a digit (0-9), or one of...

Suppose a password must have at least 9 but no more than 13 characters, where each character is a lowercase letter (a-z), a digit (0-9), or one of three special characters (!, @, #)

(a) How many different passwords are possible?

(b) How many contain at least one special character?

(c) How many contain at least one letter and at least one number?