JunikZoo

int[,] m = new int[TB_3.RowCount,TB_3.ColumnCount];
            for (int i = 0; i < TB_3.RowCount; i++)
            {
                for (int j = 0; j < TB_3.ColumnCount; j++)
                {
                    m[i, j] = Convert.ToInt32(TB_3[j, i].Value);
                    
                }
            } 
            for (int i = 0; i < TB_3.RowCount; i++)
            {
                for (int k = 0; k < TB_3.ColumnCount; k++)
                {

                    double s = 0;
                    
                    for (int j = 0; j < TB_3.ColumnCount-k; j++)
                    {
                        
                        s += m[i, k + j];
                       }
                        
                            double sum = s / (j + 1);
                            TB_2[k, i].Value = sum;
                        
                    }
                }