In one state the license plates have 6 letters so:
"XRDFGT"
or
"HAPPPY"
could be license plates (letters can repeat). How many different license plates are possible?
"HAPPPY",
Start from left, you have 26 letters to choose from for "H". Since repeats are allowed, then you have another 26 letters to choose from for "A", another 26 letters for "P".....and so on. So, in total:
You will have: 26^6 = 308,915,776 different license plates possible[Edited for typos!!]
However, some "words" may not be acceptable to authorities, such as "ROBBER" ......etc.