input: Write a python function to create a graph with X and Y axes using tkinter and Canvas object.
  assert isinstance(create_graph(tk.Tk()), tk.Canvas)
  assert create_graph(tk.Tk()).cget("width") == 480
  assert create_graph(tk.Tk()).cget("height") == 480
output: import tkinter as tk
  
  def create_graph(root):
      canvas = tk.Canvas(root, width=480, height=480)
      canvas.create_line(0, 240, 480, 240, fill="black")  # X-axis
      canvas.create_line(240, 0, 240, 480, fill="black")  # Y-axis
      canvas.pack()
      return canvas