Question: how many different number plate combinations are there?
Answer: 26 x 26 x 26 x 10 x 10 x 10 = 17,576,000. So a six-character system with three letters and three numbers can only yield, at best, 17.5 million possible plate numbers. It should be no surprise that many larger states exhausted all possible six-character combinations years ago and were forced to go to seven characters.