input: Write a python function to find the minimum and maximum numbers in a list.
  assert find_min_max([1, 3, 7, 4, 9, 0]) == (0, 9)
  assert find_min_max([10, 20, 45, 67, 84, 93]) == (10, 93)
  assert find_min_max([5, 7, 9, 8, 6, 4, 3]) == (3, 9)
output: def find_min_max(lst):
      if not lst:
          return None, None
      min_num = min(lst)
      max_num = max(lst)
      return min_num, max_num