How to draw a red line on a HTML table on a certain heighth

Question

On a bootstrap based web page I'm displaying the following table

 

This was generated with the following code:

<div class="row">
   <div class="col-lg-12">
      <div class="table-responsive">
         <table class="table table-bordered table-hover table-striped">
            <thead>
               <tr>
                  <th class="text-right success">Count</th>
                  <th class="text-right success">Lower</th>
                  <th class="text-right success">Upper</th>
                  <th class="text-right success">Price</th>
                  <th class="text-right success">Cost</th>
               </tr>
            </thead>
            <tbody>
               @foreach (var dataRow in staffelData)
               {
                  var differenceWithUpper = 0;
                  if (dataRow.Upper.HasValue)
                  {
                     differenceWithUpper = countValue - dataRow.Upper.Value;
                  }
                  else
                  {
                     differenceWithUpper = -1;
                  }
                  var cost = 0.0;
                  var inScope = 0;

                  if (differenceWithUpper >= 0)
                  {
                     inScope = dataRow.Upper.Value;
                  }
                  else
                  {
                     if (countValue >= dataRow.Lower.Value)
                     {
                        inScope = countValue - dataRow.Lower.Value;
                     }
                  }

                  cost = inScope * Decimal.ToDouble(@dataRow.PnrFee);

                  <tr>
                     <td class="text-right fit">@pnrsInScope</td>
                     @if (@dataRow.Lower.HasValue)
                     {
                        <td class="text-right fit">@dataRow.Lower.Value</td>
                     }
                     else
                     {
                        <td class="text-right fit">N/A</td>
                     }
                     @if (@dataRow.Upper.HasValue)
                     {
                        <td class="text-right fit">@dataRow.Upper.Value</td>
                     }
                     else
                     {
                        <td class="text-right fit">N/A</td>
                     }
                     <td class="text-right fit">@dataRow.Fee @dataRow.Currency</td>
                     <td class="text-right fit">@cost @dataRow.Currency</td>
                  </tr>
               }
            </tbody>
         </table>)
      </div>
   </div>
</div>

I still need 2 add 1 feature though: I have to display an average value in the same table. I was thinking to draw a line @ the level in the table the average can be found.

Could anyone here explain me how to best get this done