can't use addition assignment operator in MVC view

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.NET

Hi Friends,
i cann't do addition assignment operation in MVC view.
in this i can't do @j=@j+6;
my code is below:

 @model Tishansoft.Model.Block
@{
    var BlockList = ViewBag.BLockList as IEnumerable<Tishansoft.Model.Block>;
    var six_blocks=BlockList.Where(x=>x.BlockTypeId==3);
    Decimal count=six_blocks.Count();
    int list=Convert.ToInt16(Math.Ceiling(count/6));
    int j = 6;
    int y = 1;    
    
 }
    
 
 @foreach (var blocktype in BlockList.Where(x => x.BlockId != null))
 {
     
     
     if (blocktype.BlockTypeId == 3)
     {       
          <div class="recent-work clearfix bottom-2">     
          <div class="slidewrap1" >
          <div class="sixteen columns"> 
               <h3 class="title bottom-2">Recent Work</h3> 
          </div>
          <ul class="slider" id="sliderName1">
           
          @for (int i = 0; i < list; i++)
          {
             
              <li class="slide">              

              @foreach (var item in six_blocks.Where(x => x.BlockId <= j&&x.BlockId>=y))
              {
                   <!-- item -->
                    <div class="one-third column item">
                      <a href="@item.BlockURL.ToString()">                      
                      <img src="../Content/images/portfolio/@item.BlockImage.ToString()" alt="" class="pic" />
                      <div class="img-caption">
                      <div class="desc"><h3>@item.BlockTitle</h3><p>@item.BlockContent</p><span>+</span></div>
                      </div><!-- hover effect -->
                      </a>
                    </div>
                    <!-- End -->
              }
             
              @j=@j+6;
              @y=@y+6;
              </li>
          }
          </ul>
          </div>
          </div>
     }
 }