input: Write a python function to calculate the sum of all elements in a 2D array.
  assert sumArray([[1, 2, 3], [4, 5, 6], [7, 8, 9]]) == 45
  assert sumArray([[0, 0, 0], [0, 0, 0], [0, 0, 0]]) == 0
  assert sumArray([[1, 1], [1, 1], [1, 1]]) == 6
output: def sumArray(arr):
      return sum(sum(row) for row in arr)