• The owner of a luxury motor yacht that sails among the 4000 Greek islands charges $600/???????????????????????? per day if exactly 20 people sign up for the cruise. However, if more than 20 people sign up for the cruise (up to the maximum capacity of 90), the fare for all passengers is reduced by $4/person for each additional passenger. Assume that at least 20 people sign up for the cruise, and let x denote the number of passengers above 20. What is the revenue per day if 60 people sign up for the cruise?