diff --git a/calculator.py b/calculator.py
index a46affd..983120a 100644
--- a/calculator.py
+++ b/calculator.py
@@ -40,45 +40,85 @@
 
 
 """
-
+import traceback
 
 def add(*args):
-    """ Returns a STRING with the sum of the arguments """
+    """ Returns a STRING with the addition result of the arguments """
+    return str(int(args[0]) + int(args[1]))
+
+def sub(*args):
+    """ Returns a STRING with the subtraction result of the arguments """
+    return str(int(args[0]) - int(args[1]))
 
-    # TODO: Fill sum with the correct value, based on the
-    # args provided.
-    sum = "0"
+def mult(*args):
+    """ Returns a STRING with the multiplication result of the arguments """
+    return str(int(args[0]) * int(args[1]))
 
-    return sum
+def div(*args):
+    """ Returns a STRING with the division result of the arguments """
+    return str(int(args[0]) / int(args[1]))
 
-# TODO: Add functions for handling more arithmetic operations.
+def guide(*args):
+    """ Returns a STRING with the instructions for producing a result for the arguments """
+    body = "<h1>This is an online calculator</h1>"\
+           "To get your result, enter the address in the browser in the following format:\n"\
+           "operation/number1/number2 (i.e. add/2/4)"
+    return body
 
 def resolve_path(path):
     """
-    Should return two values: a callable and an iterable of
+    Returns two values: a callable and an iterable of
     arguments.
     """
-
-    # TODO: Provide correct values for func and args. The
-    # examples provide the correct *syntax*, but you should
-    # determine the actual values of func and args using the
-    # path.
-    func = add
-    args = ['25', '32']
+    funcs = {
+      "":guide,
+      "add":add,
+      "sum":add,
+      "sub":sub,
+      "subtract":sub,
+      "mult":mult,
+      "multiply":mult,
+      "div":div,
+      "divide":div,
+    }
+    path = path.strip('/').split('/')
+
+    func_name = path[0]
+    args = path[1:]
+
+    try:
+        func = funcs[func_name]
+    except KeyError:
+        raise NameError
 
     return func, args
 
 def application(environ, start_response):
-    # TODO: Your application code from the book database
-    # work here as well! Remember that your application must
-    # invoke start_response(status, headers) and also return
-    # the body of the response in BYTE encoding.
-    #
-    # TODO (bonus): Add error handling for a user attempting
-    # to divide by zero.
-    pass
+    headers = [("Content-type", "text/html")]
+    try:
+        path = environ.get('PATH_INFO', None)
+        if path is None:
+            raise NameError
+        func, args = resolve_path(path)
+        body = func(*args)
+        status = "200 OK"
+    except NameError:
+        status = "404 Not Found"
+        body = "<h1>Not Found</h1>"
+    except ZeroDivisionError:
+        status = "500 Inernal Server Error"
+        body = "<h1>Division by Zero Error</h1>"
+    except Exception:
+        status = "500 Internal Server Error"
+        body = "<h1>Internal Server Error</h1>"
+        print(traceback.format_exc())
+    finally:
+        headers.append(('Content-length', str(len(body))))
+        start_response(status, headers)
+        return [body.encode('utf8')]
+
 
 if __name__ == '__main__':
-    # TODO: Insert the same boilerplate wsgiref simple
-    # server creation that you used in the book database.
-    pass
+    from wsgiref.simple_server import make_server
+    srv = make_server('localhost', 8080, application)
+    srv.serve_forever()