(require 2htdp/image)
(require 2htdp/universe)

;; =================
;; Constants:

(define WIDTH 800)
(define HEIGHT 600)

(define SPEED 1)

(define TEXT-SIZE 12)
(define TEXT-COLOUR "pink")

(define MTS (empty-scene WIDTH HEIGHT))

;; =================
;; Data Definitions:

(define-struct number (x y))
;; Number is (make-drop Integer Integer)
;; interp. A number on the screen with x and y co-ordinates
(define