set selected value of one dropdown to another dropdown mvc

Question

I have  using MVC5 and have two dropdowns.When users select an item in the first dropdown I want the second dropdown to show the related item if their their ID's match. Below is my code

public JsonResult LoadTest(int id)

{

try

{

var cd = (from h in Purchases

from s in h.Schedules

where h.Id == id || h.TOId == h.Admin.TOId

&& !h.Inactive

&& !s.Finalized

&& !s.NotRequired

)

orderby s.DateSort

select h).Distinct();

var cSelectItems = cd

.Distinct()

.Select(item => new SelectListItem

{

Text = item.Number + "/" + item.Name,

Value = item.Id.ToString( )

});

ViewData["Class"] = cdrlSelectItems;

foreach (var t in cd)

{

if(t.TOId > 0)

{

var wto = (from h in Purchases

from s in h.Schedules

where h.Id == id && h.TOId == h.Admin.TOId

&& !h.Inactive

&& !s.Finalized

&& !s.NoLongerRequired

)

orderby s.DateSort

select h).Distinct();

var cWdtoSelect = wto

.Distinct()

.Select(item => new SelectListItem

{

Text = item.Number + "/" + item.CName,

Selected = item.Id == t.TOId,

Value = item.Id.ToString( )

});

return Json(cWdtoSelect.ToList(), JsonRequestBehavior.AllowGet);

}

}

return Json(cSelectItems.ToList(), JsonRequestBehavior.AllowGet);

}

catch (Exception ex)

{

throw;

}