--- a/app.py
+++ b/app.py
@@ -1,5 +1,8 @@
+def _total(price, shipping, discount):
+    return round(price * discount + shipping, 2)
+
 def guest_total(price, shipping):
-    return round(price + shipping, 2)
+    return _total(price, shipping, 1)
 
 def member_total(price, shipping):
-    return round(price * 0.9 + shipping, 2)
+    return _total(price, shipping, 0.9)