HttpClient Post request arise an error?

Question

 

 I am write a code as bellow for using windows phone :

 

private void Btn_Submit_Click(object sender, RoutedEventArgs e)

        {

            string urlPath = "http://192.168.1.84/manageit/servlet/uidServlet";

            using (HttpClient hc = new HttpClient(new HttpClientHandler()))

            {

                var values = new List<KeyValuePair<string, string>>

                {

                    new KeyValuePair<string, string>("ticketId",tb_TicketNo.Text),

                    new KeyValuePair<string, string>("status","test"),

                    new KeyValuePair<string, string>("responseTime","test"),

                    new KeyValuePair<string, string>("clouserComment","test"),

                    new KeyValuePair<string, string>("date_time","test"),

                    new KeyValuePair<string, string>("lat","test"),

                    new KeyValuePair<string, string>("longitude","test"),

                    new KeyValuePair<string, string>("barcode","test"),

                    new KeyValuePair<string, string>("CustName","test"),

                    new KeyValuePair<string, string>("CustDesignation","test"),

                    new KeyValuePair<string, string>("user_id","test"),

                    new KeyValuePair<string, string>("remark","test"),

                    new KeyValuePair<string, string>("observation_date","test")

                };

                var content = new FormUrlEncodedContent(values);

                var response = await hc.PostAsync(urlPath, content);

            }

        }

But  await hc.PostAsync(urlPath, content);  Aries an error is

 

"The 'await' operator can only be used within an async method. Consider marking this method with the 'async' modifier and changing its return type to 'Task'."