input: def averageMatrix(matrix):
      """
      Calculate the average of all 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
      count = 0
      for row in matrix:
          for e in row:
              sum += e
              count += 1
  
      return round(sum / count, 2)