;; Constants
(define PERFORMANCE-COST 180)
(define ATTENDEE-COST 0.04)
(define PEOPLE-ATTEND 120)
(define INCREASE-ATTENDANCE 15)
(define PRICE-DECREASE 0.10)
(define PRICE-PER-TICKET 5.00)


;; How to design a program 
(define (profit ticket-price)
  (- (revenue ticket-price)
     (cost ticket-price)))

(define (revenue ticket-price)
  (*  (attendees ticket-price) ticket-price))

(define (cost ticket-price)
  (+ PERFORMANCE-COST 
     (* ATTENDEE-COST (attendees ticket-price))))

(define (attendees ticket-price)
  (+ PEOPLE-ATTEND
     (* (/ INCREASE-ATTENDANCE PRICE-DECREASE) (- PRICE-PER-TICKET ticket-price))))