Assume that pssword for computer system should have at least five, but no more than fifteen, characters, where every character in password is lowercase English letter, uppercase English letter, digit, or one of 6 special characters ?, >, <, !, +, and =.
i) Find number of different passwords are available for computer system?
ii) Find number of the passwords has at least one occurrence of at least one of 6 special characters?
iii) Using the answer to part (a), Find how long it takes the hacker to try every feasible password, suppose that it takes one nanosecond for the hacker to check possible password.