Filter Generic List items based in ASP.Net ListBox value using LINQ Query

Use StartsWith and pass the data to where condition in the linq query to filter the record.

public List<Header> GetOpen(string ddl0)
{
    List<Header> Result = (from t in context.Headers
                           where t.IsActive == true && t.Id.StartsWith(ddl0)
                           select t).ToList();
    return Result;
}