input: def averageMatrix(matrix):
      """ Calculate the average of the elements in a 2-dimensional array.
      >>> averageMatrix([[3,2,6], [8,5,9], [4,7,1]])
      4.77
      """
      sum = 0
      for row in matrix:
          for e in row:
              sum += e
      return sum / (len(matrix) * len(matrix[0]))
output:     sum = 0
      for row in matrix:
          for e in row:
              sum += e
      return round(sum / (len(matrix) * len(matrix[0])), 2)