Referencing System.Data.DataSetExtensions.dll

I need to reference to System.Data.DataSetExtensions.dll to use Linq To DataSet

I am running this piece of code:
DataTable dt = _dataSetCache.Tables[“table0”];

var query = from d in dt.AsEnumerable()
                    orderby d.Field<int>("INSTANCES")
                    select d;

and getting this error

The type arguments for method
cannot be inferred from the usage. Try
specifying the type arguments

How do I reference to make AsEnumerable available for my datatable in unity

The issue isn’t with referencing the .dll. The issue is your use of it. Since I don’t have that library, I can only guess that it wants this:

 var query = from d in dt.AsEnumerable(this.dt)
                     orderby d.Field<int>("INSTANCES")
                     select d;