7. [7] A bank wants to allow customers to use personal identification numbers (PINS) for their ATM which are six characters long, using hexadecimal characters instead of only decimal digits. The

hexadecimal system includes 16 characters, with the decimal values 0-9 and the letters A-F. a. How many different PIN combinations are possible if there are no restrictions on selecting characters? How many different PIN combinations are possible if the first position needs to be a letter and the last position needs to be a decimal value (0-9)? b. How many different PIN combinations are possible if no character can be repeated and the characters must alternate between letters and numbers? Hint: you could start with either a letter or a digit. C.