Hi guys! I'm doing math and I've stumbled upon a question I don't know how to answer. I have the answer but I don't know how to get it. An explanation would be great, thanks.

Also, please note that NSW is New South Wales (AUS) and the next three digits are numbers.

A witness described a getaway car as having a NSW registration plate starting with TLK. The witness could not remember the three digits that followed, but recalled that all three digits were different. How many cars in NSW could have a registration plate with these letters and numbers?