I created picking module and now I need help in subtract/minus Demanded Qty to the Qty from the wms table based on the lot number selected and it will happen only when the checkbox was check.

Here is the flow:

1. Select SR #
2. After Select SR # data will display below
3. Choose Lot Number
4. Check the beside textbox to subtract/minus the demanded qty to the lot number qty from wms table
5. When the check box was check and after subtract the select option will be only display the lot number you selected.

I am new in using checkbox.

Here is my code:

   date_default_timezone_set("Asia/Singapore"); //set the time zone  
$con = mysql_connect('localhost', 'root','');

if (!$con) {
    echo 'failed';

mysql_select_db("mes", $con);
$Date_Shelve =date('Y-m-d H:i:s');
<link href="kanban.css" rel="stylesheet" type="text/css">

<script type="text/javascript">
function get_option(elm){
  var elm = document.getElementById('sr_number');
sr_number = elm.options[elm.selectedIndex].value;



<div id="SR_date">
<label>Date :</label>
<input type="text" name="date_pick" value="<?php echo $Date_Shelve; ?>" size="16" readonly="readonly" style="border: none;">    

 <div id="Picking">
<label class="LLabellot">Select SR # :</label>
$query = "SELECT DISTINCT m.sr_number FROM sr_main m JOIN sr_submain s ON (m.sr_number = s.sr_number)  ORDER BY sr_number";                 
$rows = mysql_query($query, $con);        
 echo "<select name = 'sr_number' onchange='get_option();'>";                
  echo "<option> Select </option>";
  while ($record = mysql_fetch_array($rows))          
      echo "<option value = '{$record['sr_number']}'";             
      if ($lot_number == $record['sr_number'])                 
      echo "selected = 'selected'";             
       echo ">{$record['sr_number']}</option>";        
  echo "</select>";    
  echo "<br/><br/>";     

  $sr_number = $_POST['sr_number'];
$sql = "SELECT sr_number, Items, DemandedQty, uom 
FROM sr_main WHERE sr_number = '$sr_number'";
$res_sr_main = mysql_query($sql, $con);

$row_num = mysql_num_rows($res_sr_main);

if($row_num > 0){

while($row_sr_main = mysql_fetch_assoc($res_sr_main)){

$sr_number = $row_sr_main['sr_number'];
$items = $row_sr_main['Items'];
$demandedqty = $row_sr_main['DemandedQty'];
$uom = $row_sr_main['uom']; 
echo "<form name='picking_form' action='' method='post'> ";   
echo "<label> SR # :</label>";
echo $sr_number;

echo "<table>";
echo "<th>Items</th>
        <th> Item Code </th>
        <th> Demanded Qty </th>
        <th> UoM </th>
        <th> Description </th>
        <th> Lot Number </th>
        <th> Approve</th>";
echo "<tr>
        <td style='text-align:right;'>$demandedqty</td>
$sql_sub = "SELECT sr_number, Items, ItemCode, SubQty, UoM, Description 
FROM sr_submain WHERE sr_number = '$sr_number' and Items = '$items'";
$res_sub = mysql_query($sql_sub, $con); 

while($row_sub = mysql_fetch_assoc($res_sub)){
  $sr_num = $row_sub['sr_number'];
  $Items = $row_sub['Items'];
  $ItemCode = $row_sub['ItemCode'];
  $SubQty = $row_sub['SubQty'];
  $UoM = $row_sub['UoM'];
  $Description = $row_sub['Description'];

$query = "SELECT lot_number from wms WHERE (date_shelve IS NOT NULL) ORDER BY lot_number";                 
$rows = mysql_query($query, $con);  
 echo "<tr>
        <td style='text-align:right;'>$SubQty</td>
 echo "<td><select name = 'lot_number'>";
 echo "<option> Select </option>";                
  while ($record = mysql_fetch_array($rows))          
      echo "<option value = '{$record['lot_number']}'";             
      if ($lot_number == $record['lot_number'])                 
      echo "selected = 'selected'";             
       echo ">{$record['lot_number']}</option>";        
  echo "</select>";    
     echo "<td><input type='checkbox' name='chk' value=''></td>
Thank you so much