input: Write a function that adds two numbers and then doubles the result.
  
  ### Output:
  def double_add(num1, num2): 
      return (num1 + num2) * 2
  
  assert double_add(1, 2) == 6
  assert double_add(3, 4) == 14
  assert double_add(-1, -1) == -4
  assert double_add(0, 0) == 0
output: def double_add(num1, num2): 
      return (num1 + num2) * 2