Using and Creating helper in Asp.net MVC4 Web Application

I am using the Asp.net mvc4 WebRole, and I found this is a Web Application , Not a Web Site. after reading this article, I knew how to add customer Helper function in Asp.MVC4. In Web Site Appliction I can add a cshtml file in app_code folder like below so that I can use my custom helper method in another cshtml.

  @helper  HotDeployButton(string value, string url , bool enable= true){

      string enablestr = string.Empty;
      if (!enable)
      {
          enablestr = "disabled=\"disabled\"";
      }

      <input type="button"  name="@value" value="@value" onclick=" window.location.href='@url'" class="mobile-button"  @enablestr />
  }

  @helper Img(string picName, string alt ){

      string root = "/content/themes/default/images/";
      string imgurl = root + picName;

      <img  alt="@alt" src="@imgurl" title="@alt" />

  }

In Another cshtml shown below will use HotDeployButton method.

<div class="bottom-div">
            @Html.Hidden("hdSelMinorPackId", "")
            <!--Html.Hidden("randomId", (object)ViewBag.RandomId)-->
            <input type="submit" name="ExcuteDeploy" id="ExcuteDeploy" value="Deploy" onclick="return validateVersion();"
                class="mobile-button" />
            &nbsp;&nbsp;&nbsp;&nbsp;
            @Helpers.HotDeployButton("Back", Url.Action("Index"))
        </div>

But in Asp.net Web Application there is no App_code Folder in project. I don't know how to make it in a Web Application . please help me .Thanks