input: Write a function to concatenate two lists and return the sum of their elements.
  assert concatenate_and_sum([1, 2, 3], [4, 5, 6]) == 21
  assert concatenate_and_sum([10, 20], [30, 40]) == 100
  assert concatenate_and_sum([7, 8], [9, 10, 11]) == 45
output: def concatenate_and_sum(list1, list2):
      concatenated_list = list1 + list2
      return sum(concatenated_list)