;; The first three lines of this file were inserted by DrScheme. They record metadata
;; about the language level of this file in a form that our tools can easily process.
#reader(lib "htdp-beginner-reader.ss" "lang")((modname 4.4.3) (read-case-sensitive #t) (teachpacks ((lib "convert.ss" "teachpack" "htdp"))) (htdp-settings #8(#t constructor repeating-decimal #f #t none #f ((lib "convert.ss" "teachpack" "htdp")))))
(define BRACKET2 500)
(define BRACKET3 1500)
(define BRACKET4 2500)
(define BRACKETRATE1 0.0025)
(define BRACKETRATE2 0.0050)
(define BRACKETRATE3 0.0075)
(define BRACKETRATE4 0.0100)

;; pay-back : number -> number
;; Calculates the pay back rate based on the charge on the credit card

(define (pay-back charges)
  (cond
    [(<= charges BRACKET2) (* BRACKETRATE1 charges)]
    [(<= charges BRACKET3) (+
                            (* BRACKETRATE2 (- charges BRACKET2))
                            (* BRACKETRATE1 BRACKET2))]
    [(<= charges BRACKET4) (+
                            (* BRACKETRATE3 (- charges BRACKET3))
                            (* BRACKETRATE2 (- BRACKET3 BRACKET2))
                            (* BRACKETRATE1 BRACKET2))]
    [(> charges BRACKET4) (+
                           (* BRACKETRATE4 (- charges BRACKET4))
                           (* BRACKETRATE3 (- BRACKET4 BRACKET3))
                           (* BRACKETRATE2 (- BRACKET3 BRACKET2))
                           (* BRACKETRATE1 BRACKET2))]))