You can use two different ways to retrieve items from a database. The first one is uses the DataContext to call the stored procedure and in a LINQ syntax:
NorthwindDataContext db = new NorthwindDataContext();
var results = from item in db.CustOrderHist("category")
where item.Total > 10
and the second way is to use the extension with a lumbda expression:
results = db.CustOrderHist("category")
.where (item => Item.Total > 10);
I still havn't figure out which one has which benefits comparing the other way.