Express this question by using difference equation and then solve the equation by using a generating function. Sam creates a computer virus and installs it on a single computer at 00:01 on day 0. When the virus first infects a computer it initially confines its activity to copying all the files on the computer,but exactly two days later it infects 20 previously uninfected other computers and infects 20 more previously uninfected computers every 24 hours after that. How many computers are infected at midday n days later.