public ActionResult Multiplicar(Calcular datos)
 {
     ViewBag.r = datos.a * datos.b;
       return this.View();
 }
 public ActionResult Sumar(Calcular datos)
 {
     ViewBag.r = datos.a + datos.b;
     return this.View();
 }
 public ActionResult Dividir(Calcular datos)
 {
     ViewBag.r = datos.c / datos.d;
       return this.View();
 }