A hacker is trying to guess someone's password. The hacker knows $($somehow$)$ that the password is $12$ characters long, and that each character is either a lowercase letter, $($a$,$ b$,$ c$,$ etc$),$ an uppercase letter $($A$,$ B$,$ C$,$ etc$)$ or a numerical digit $(0,1,2,3,4,5,6,7,8,$ or $9).$ Assume that the hacker makes random guesses.