A recent survey asked 90 students "How many hours do you spend on the computer in a typical day?" Of the 90 respondents 3 said 1 hour, 5 said 2 hours, 15 said 3 hours, 25 said 4 hours, 20 said 5 hours, 15 said 6 hours, 5 said 7 hours 1 said 8 hours and 1 said 9 hours. What is the average (mean) number of hours spent on the computer?