input: Write a python function to find the maximum number in a list.
  assert find_max_number([7, 4, 5, 100, 2]) == 100
  assert find_max_number([1, 2, 3, 4, 5]) == 5
  assert find_max_number([-10, -20, -30, -5]) == -5
output: def find_max_number(lst):
      if not lst:
          raise ValueError("List is empty")
      max_num = lst[0]
      for num in lst:
          if num > max_num:
              max_num = num
      return max_num