How do I input 2 numbers and add them via .net web service I already made ,in android studio ,,please help me

import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;

import android.os.AsyncTask;
import android.app.Activity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;


import org.ksoap2.SoapEnvelope;
import org.ksoap2.serialization.PropertyInfo;
import org.ksoap2.serialization.SoapObject;
import org.ksoap2.serialization.SoapPrimitive;
import org.ksoap2.serialization.SoapSerializationEnvelope;
import org.ksoap2.transport.HttpTransportSE;



public class MainActivity extends Activity {

    private final String NAMESPACE = "http://tempuri.org/Webservice";
    private final String URL = "http://localhost:28013/CalculatorWebService.asmx";
    private final String SOAP_ACTION = "http://tempuri.org/Webservice/Add";
    private final String METHOD_NAME = "Add";
    private String TAG = "PGGURU";
    private static String fstNumber;
    private static String secNumber;
    private static String ans;
    Button b;
    EditText fn;
    EditText sn;
    TextView tv ;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        fn = (EditText) findViewById(R.id.et1);
        sn = (EditText) findViewById(R.id.et2);
        tv = (TextView) findViewById(R.id.tv_result);

        b = (Button) findViewById(R.id.btn);

        b.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                //Check if FirstNumber text control is not empty
                if (fn.getText().length() != 0 && fn.getText().toString() != "") {
                    //Get the text control value
                    fstNumber = fn.getText().toString();
                    //Create instance for AsyncCallWS
                    AsyncCallWS task = new AsyncCallWS();
                    //Call execute
                    task.execute();
                    //If text control is empty
                } else {
                    tv.setText("Please enter some numbers");
                }
                if (sn.getText().length() != 0 && sn.getText().toString() != "") {
                    //Get the text control value
                    secNumber = sn.getText().toString();
                    //Create instance for AsyncCallWS
                    AsyncCallWS task = new AsyncCallWS();
                    //Call execute
                    task.execute();
                    //If text control is empty
                } else {
                    tv.setText("Please enter some numbers");
                }
            }

        });

    }

    public void getAdd(String firstNumber, String secondNumber) {
        //Create request
        SoapObject request = new SoapObject(NAMESPACE, METHOD_NAME);

        //Property which holds input parameters
        PropertyInfo PI = new PropertyInfo();
        //Set Names
        PI.setName("firstNumber");
        //Set Values
        PI.setValue(firstNumber);
        //Set dataType
        PI.setType(Double.class);
        //Add the property to request object
        request.addProperty(PI);
        // second Property which holds input parameters
        PI = new PropertyInfo();
        //Set Names
        PI.setName("secondNumber");
        //Set Values
        PI.setValue(secondNumber);
        //Set dataType
        PI.setType(Double.class);
        //Add the property to request object
        request.addProperty(PI);
        //Create envelope
        SoapSerializationEnvelope envelope = new SoapSerializationEnvelope(
                SoapEnvelope.VER11);
        envelope.dotNet = true;
        //Set output SOAP object
        envelope.setOutputSoapObject(request);
        //Create HTTP call object
        HttpTransportSE androidHttpTransport = new HttpTransportSE(URL);


        try {
            //Involve web service
            androidHttpTransport.call(SOAP_ACTION, envelope);
            //Get the response
            SoapPrimitive response = (SoapPrimitive) envelope.getResponse();
            //Assign it to ans static variable
            ans = response.toString();


        } catch (Exception e) {
            e.printStackTrace();
        }
    }



    private class AsyncCallWS extends AsyncTask<string,> {




        @Override
        protected Void doInBackground(String... params) {
            
            Log.i(TAG, "doInBackground");
            getAdd(fstNumber,secNumber);
            return null;
        }

        @Override
        protected void onPreExecute() {
            Log.i(TAG, "onPreExecute");
            tv.setText("Calculating...");
        }

        @Override
        protected void onPostExecute(Void result) {
            super.onPostExecute(result);
            Log.i(TAG, "onPostExecute");
            tv.setText(ans + "is the answer");
        }



        @Override
        protected void onProgressUpdate(Void... values) {
            Log.i(TAG, "onProgressUpdate");
        }

    }