



 
Hi, You have a total of $26 + 10 = 36$ characters and you want to form 8 character words. Think about making a list of all the 8 character words. Start with one character words. There are 36 of them. Each of them can be expanded to a two character word by appending a second character. Since there are 36 possibilities for the second character you have $36 \times 36 = 36^2$ two character words. Each of the $36^2$ two character words can be expanded to a three character word by appending a third character. Hence there are $36^2 \times 36 = 36^3$ three character words. And so on,  


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