input: Write a python function to find a pair of numbers in a list that sum up to a given target.
  assert findPair([2, 4, 6, 8], 10) == (2, 8)
  assert findPair([1, 2, 3, 9], 10) == (1, 9)
  assert findPair([5, 5, 5, 5], 10) == (5, 5)
output: def findPair(numbers, target):
      seen = set()
      for number in numbers:
          complement = target - number
          if complement in seen:
              return (complement, number)
          seen.add(number)