input: def largest_three_numbers(my_list: List[int]) -> List[int]:
      """
      Find the largest three numbers in a given list of integers.
      
      >>> largest_three_numbers([1, 6, 3, 8, 7, 4])
      [6, 7, 8]
      """
output:     my_list.sort(reverse=True)
      return my_list[:3]