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