input: Write a python function to find a pair of numbers in a list that add up to a given target sum.
  assert find_pair_with_sum([2, 3, 4, 5], 5) == [2, 3]
  assert find_pair_with_sum([1, 2, 3, 9], 10) == [1, 9]
  assert find_pair_with_sum([0, -1, 2, -3, 1], -2) == [-3, 1]
output: def find_pair_with_sum(numbers, target_sum):
      seen = set()
      for number in numbers:
          complement = target_sum - number
          if complement in seen:
              return [complement, number]
          seen.add(number)
      return None