input: Write a function to plot multiple lines on a graph with legends using matplotlib.
  assert plot_multilines([[1, 2, 3, 4], [1, 2, 3, 4]], [[2, 4, 6, 8], [3, 6, 9, 12]]) is None
output: def plot_multilines(x_data, y_data):
      import matplotlib.pyplot as plt
      
      for x, y in zip(x_data, y_data):
          plt.plot(x, y)
      
      plt.legend([f'Line {i+1}' for i in range(len(x_data))])
      plt.show()