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diff --git a/coding-exercises/2/30.rkt b/coding-exercises/2/30.rkt
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+++ b/coding-exercises/2/30.rkt
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+#lang racket
+(define (scale-tree tree factor)
+  (cond ((null? tree) nil)
+        ((not (pair? tree)) (* tree factor))
+        (else (cons (scale-tree (car tree) factor)
+                    (scale-tree (cdr tree) factor)))))
+
+(define (scale-tree tree factor)
+  (map (lambda (sub-tree)
+         (if (pair? sub-tree)
+           (scale-tree subtree factor)
+           (* sub-tree factor)))
+       tree))
+
+;; analogous to, but we now also have to test when to recurse in the middle of the tree
+;; (define (square-list items)
+;;   (if (null? items)
+;;     (list)
+;;     (cons (square (car items)) (square-list (cdr items)))))
+(define (square-tree tree)
+  (cond ((null? tree) nil)
+        ((not (pair? tree)) (* tree tree))
+        (else (cons (square-tree (car tree))
+                    (square-tree (cdr tree))))))
+
+(define test-tree (list 1 (list 2 (list 3 4) 5) (list 6 7)))
+((lambda ()
+   (display (square-tree test-tree))))
+
+;; Can I also pass some state combining sequence and recursive operations?
+(define (square-tree-map tree)
+  (map (lambda (subtree)
+         (if (pair? subtree)
+           (square-tree-map subtree)
+           (* subtree subtree)))
+       tree))
+((lambda ()
+   (display (square-tree-map test-tree))))