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