A hacker's 'dictionary' contains 650,000 passwords which he obtained on the Darknet. He has gained access to 500,000 usernames for a particular target site. He is going to try all the possible combinations of the passwords with all of the usernames using a brute-force attack. His computer system can test 1 billion (109) combinations per second. How long will it take him to check all the passwords against all the usernames? Give your answer in seconds correct to 2 significant figures. Show all your working clearly in a way that will help your tutor understand how you arrived at your