Beginner in need of help with command
Hello all, I'm trying to crack a RAR3 file and I'm looking for some guidance with specific rules.

What I want to do is specify a starting phrase and character sets. 
To give an example, I know that the password starts with "ExamplePhrase" followed by unknown characters that are either uppercase or lowercase letters "A-Z" and "a-z". 
Ex: "ExamplePhraseXxxxxXxxxxxXxxxx" 
Where 'x' are the unknown letters/words that need to be cracked. 

Basically, what I need help with is what command to write in order to specify the starting phrase and character sets. 

I know this isn't going to do it but what I have so far is:
 hashcat -a 3 -m 12500 rarhash.txt