Add geometry section to Python turtle activity. (#460)

Co-authored-by: Oliver Zhang <[email protected]>

content/english/python-turtle/activity-3.md

@@ -11,6 +11,16 @@ Great job! You just drew your first shape in Python with Turtle! Now let’s sli
 
 To help you draw a hexagon, think of how many sides a hexagon has. How many degrees are in each angle of a hexagon?
 
+{{% expand "**Hint:**" %}} 
+Remember that in any shape, all the angles add up to 360°. For example, there are 4 sides in a square, so each angle of a square is 360 ÷ 4 = 90°.
+{{% /expand %}}
+<br/>
+
+{{% expand "**Show answer:**" %}} 
+As a hexagon have 6 sides, each angle of a hexagon is 360 ÷ 6 = 60°.
+{{% /expand %}}
+<br/>
+
 As a helpful reminder, this is the code that was used to create a triangle:
 
 ``` python