input: Write a python function to add and subtract two 2D vectors using a class.
  assert (Vector2D(1, 2).add(Vector2D(3, 4)), (Vector2D(1, 2).subtract(Vector2D(3, 4)))) == ((4, 6), (-2, -2))
  assert (Vector2D(5, 7).add(Vector2D(2, 3)), (Vector2D(5, 7).subtract(Vector2D(2, 3)))) == ((7, 10), (3, 4))
  assert (Vector2D(0, 0).add(Vector2D(0, 0)), (Vector2D(0, 0).subtract(Vector2D(0, 0)))) == ((0, 0), (0, 0))
output: class Vector2D:
      def __init__(self, x, y):
          self.x = x
          self.y = y
  
      def add(self, other):
          return (self.x + other.x, self.y + other.y)
  
      def subtract(self, other):
          return (self.x - other.x, self.y - other.y)