Problem
A point is defined as (define-struct posn (x y))
;; x and y are numbers
A Polygon shape is a (listof posn)
Write a function largest-x that consumes shape1 which is a non-empty (listof Posn), and produces the largest x-coordinate of any posn in the list. Use Dr. Racket and you can use recursion or abstract list function (use only map, filter, folder, or sort).