input: Write a python function to keep track of the values x, y, and z, and return them as a tuple. 
  assert keep_track([("x", 1), ("y", 2), ("z", 3)]) == (1, 2, 3)
  assert keep_track([("x", 1), ("x", 2), ("z", 4)]) == (2, 0, 4)
  assert keep_track([("y", 5), ("z", 2), ("x", 1)]) == (1, 5, 2)
output: def keep_track(operations):
      values = {"x": 0, "y": 0, "z": 0}
      
      for var, val in operations:
          values[var] = val
      
      return (values["x"], values["y"], values["z"])