hard q30: add solution png and correct code

q30/shapes.py

@@ -1,14 +1,22 @@
 class Shape:
     def area(self):
-        return 0
+        return
 
 class Circle(Shape):
+    def __init__(self, r):
+        self.r = r
+
     def area(self):
-        return 3.14 * r * r
+        return 3.14 * self.r * self.r
 
 class Square(Shape):
+    def __init__(self, side):
+        self.side = side
+
     def area(self):
-        return side * side
+        return self.side * self.side
 
 if __name__ == '__main__':
-    
+    shapes = [Circle(3), Square(5)]
+    for s in shapes:
+        print(s.area())