input: Write a python function to sum two arrays element-wise.
  assert sum_arrays([1, 2, 3], [4, 5, 6]) == [5, 7, 9]
  assert sum_arrays([0, 0, 0], [1, 2, 3]) == [1, 2, 3]
  assert sum_arrays([10, 20, 30], [1, 2, 3]) == [11, 22, 33]
output: def sum_arrays(arr1, arr2):
      return [a + b for a, b in zip(arr1, arr2)]