The owner of a luxury motor yacht that sails among the 4000 greek islands charges $700/person per day if exactly 20 people sign up for the cruise. however, if more than 20 people (up to the maximum capacity of 90) sign up for the cruise, then each fare is reduced by $5/person for each additional passenger. assume at least 20 people sign up for the cruise, and let x denote the number of passengers above 20.

(a) find a function r giving the revenue per day realized from the charter.
r(x) =

(b) what is the revenue per day if 55 people sign up for the cruise?

(c) what is the revenue per day if 65 people sign up for the cruise?