How does the vehicle model specify?

Including letters and numbers, numbering principle, it is best to explain clearly points

Now is 2 in the choice: 1): 4 digits + 1 letters. Rules are 3,6,8,9 The same number can not be repeated, the first four digits of the last letter (L to Z) 2): 2 letters + 3 digits. Rules are 3,6,8,9 The same number can not be repeated. The first is the letter, the middle three numbers, the last letter.