datediff with case statement in select query linq

Question

select case statement in linq query.

Here is the query on sql:

select case when DATEDIFF(day,convert(varchar,Min([Order].CreatedOnUtc),101),convert(varchar,Max([Order].CreatedOnUtc),101)) = 0 then
 Sum([Order].OrderSubtotal)
 else
 case when (DATEDIFF(day,convert(varchar,Min([Order].CreatedOnUtc),101),convert(varchar,Max([Order].CreatedOnUtc),101))/30) = 0 then Sum([Order].OrderSubtotal) else
 Sum([Order].OrderSubtotal)/
  (DATEDIFF(day,convert(varchar,Min([Order].CreatedOnUtc),101),convert(varchar,Max([Order].CreatedOnUtc),101))/30)
 end
 end as 'Account Value' from [order] where And Account.ID = @Act_ID

I am trying the code here:

var query = _orderRepository.Table;
       query = query.Where(o => o.AccountId == accountId);

In query i am getting my value.

After query statement what should i write?? how do i write for case statement using linq???