สอบถาม ajax บวกเลขอัตโนมัติ2ชั้น ดูจากภาพน่าจะเข้าใจง่ายกว่า จากโค้ดนะครับ ผมเขียนโค้ดจัดเรียงไม่สวย

<!-- เพิ่มสินค้า -->
		<script language="javascript">
			function CreateNewRow()
			{
				var intLine = parseInt(document.frmMain.hdnMaxLine.value);
				intLine++;
					
				var theTable = document.all.addorder
				var newRow = theTable.insertRow(theTable.rows.length)
				newRow.id = newRow.uniqueID
				
				var item1 = 1
				var newCell

				//*** Column 0 ***//
				newCell = newRow.insertCell(0)
				newCell.id = newCell.uniqueID
				newCell.setAttribute("className", "css-name");
				newCell.innerHTML = "<div class=\"col-md-12 column\">"+intLine+"</div><div class=\"col-md-12 column\"><br/></div>"
				
				//*** Column 1 ***//
				newCell = newRow.insertCell(1)
				newCell.id = newCell.uniqueID
				newCell.setAttribute("className", "css-name");
				newCell.innerHTML = "<div class=\"col-md-12 column\"><input name=\"iditem"+intLine+"\" type=\"text\" class=\"form-control\" id=\"iditem"+intLine+"\" value=\"iditem"+intLine+"\" ></div><div class=\"col-md-12 column\"><br/></div>"

				//*** Column 2 ***//
				newCell = newRow.insertCell(2)
				newCell.id = newCell.uniqueID
				newCell.setAttribute("className", "css-name");
				newCell.innerHTML = "<div class=\"col-md-12 column\"><input name=\"Price"+intLine+"\" type=\"text\" class=\"form-control\" id=\"Price"+intLine+"\" disabled value=\""+Math.floor((Math.random() * 100) + 10)+"\" ></div><div class=\"col-md-12 column\"><br/></div>"
				
				//*** Column 3 ***//
				newCell = newRow.insertCell(3)
				newCell.id = newCell.uniqueID
				newCell.setAttribute("className", "css-name");
				newCell.innerHTML = "<div class=\"col-md-12 column\"><input name=\"Volume"+intLine+"\" type=\"text\" class=\"form-control\" id=\"Volume"+intLine+"\" value=\"\" placeholder=\"0\" onkeyup=\"sum("+intLine+")\"></div><div class=\"col-md-12 column\"><br/></div>"

				//*** Column 4 ***//
				newCell = newRow.insertCell(4)
				newCell.id = newCell.uniqueID
				newCell.setAttribute("className", "css-name");
				newCell.innerHTML = "<div class=\"col-md-12 column\"><input name=\"total"+intLine+"\" type=\"text\" class=\"form-control\" id=\"total"+intLine+"\"  value=\"0\" disabled ></div><div class=\"col-md-12 column\"><br/></div>"

				document.frmMain.hdnMaxLine.value = intLine;
			}
			
			function RemoveRow()
			{
				intLine = parseInt(document.frmMain.hdnMaxLine.value);
				if(parseInt(intLine) > 0)
				{
						theTable = (document.all) ? document.all.addorder : 
						document.getElementById("addorder")
						theTableBody = theTable.tBodies[0];
						theTableBody.deleteRow(intLine);
						intLine--;
						document.frmMain.hdnMaxLine.value = intLine;
				}	
			}	

			function sum(n) {
			var num_1 = $("#Price"+n).val();
			var num_2 = $("#Volume"+n).val();
			var num_result = "";
			
					$.ajax({
						type : "POST",
						url : "b.php",
						data : "num_1="+num_1+"&num_2="+num_2,
						cache:false,
						success: function(data) {
							$("#total"+n).val(data);	
						}
					})
					
				}

			

		</script>

<div class=\"col-md-12 column\">
											<form name=\"frmMain\" method=\"post\">
												<table border=\"1\" id=\"addorder\">
												  <tr>
													<td><div class=\"col-md-12 column\">ลำดับ</div></td>
													<td><div class=\"col-md-12 column\">รหัสสินค้า-ชื่อสินค้า</div></td>
													<td><div class=\"col-md-12 column\">ราคา/หน่วย</div></td>
													<td><div class=\"col-md-12 column\">จำนวน</div></td>
													<td><div class=\"col-md-12 column\">รวม</div></td>
												  </tr>
												</table>
												<input type=\"hidden\" name=\"hdnMaxLine\" value=\"0\">
													<button type=\"button\" name=\"btnAdd\" class=\"btn btn-success\" id=\"btnAdd\" onClick=\"CreateNewRow();\">+เพิ่ม</button>
													<button type=\"button\" name=\"btnDel\" class=\"btn btn-danger\" id=\"btnDel\" onClick=\"RemoveRow();\">-ลบ</button>
												</form>
											</div>


<div class=\"col-md-12 column\"><br/></div>
											<div class=\"col-md-4 column\">
												<label for=\"DocTotal\">DocTotal</label><input name=\"DocTotal\" type=\"text\" class=\"form-control\" id=\"DocTotal\" disabled value=\"0\" >
											</div>
											<div class=\"col-md-12 column\"><br/></div>