Как передать значение кнопок в переменную и сложить их

У кнопок TogleButton есть определённое значение, если она нажата, то значение передаётся в переменную double a или double d. Нужно сложить эти значения и вывести в TextView. При запуске кода сейчас выводит 0.00

package space.l3n04k4.myapplication;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.widget.CompoundButton;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.ToggleButton;

public class kvartira extends AppCompatActivity{

    ToggleButton one;
    ToggleButton two;
    ToggleButton three;
    ToggleButton four;
    ToggleButton five;
    ToggleButton six; 
    ToggleButton btn13;
    ToggleButton btn14;
    ToggleButton btn15;
    TextView result;
    double a;
    double SummaA(double a){
        return a;
    }
    double d;
    double SummaD(double d){
        return d;
    }
    double itog = SummaA(a) + SummaD(d);
    String res = Double.toString(itog);

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_kvartira); 
        result = findViewById(R.id.result);
        result.setText(res);

        one = findViewById(R.id.toggleButton3);
        two = findViewById(R.id.toggleButton4);
        three = findViewById(R.id.toggleButton5);
        four = findViewById(R.id.toggleButton6);
        five = findViewById(R.id.toggleButton7);
        six = findViewById(R.id.toggleButton8);
        btn13 = findViewById(R.id.btn13);
        btn14 = findViewById(R.id.btn14);
        btn15 = findViewById(R.id.btn15);

        one.setOnCheckedChangeListener(changeChecker);
        two.setOnCheckedChangeListener(changeChecker);
        three.setOnCheckedChangeListener(changeChecker);
        four.setOnCheckedChangeListener(changeChecker);
        five.setOnCheckedChangeListener(changeChecker);
        six.setOnCheckedChangeListener(changeChecker);
        btn13.setOnCheckedChangeListener(changeChecker3);
        btn14.setOnCheckedChangeListener(changeChecker3);
        btn15.setOnCheckedChangeListener(changeChecker3);
        one.setChecked(true);
        btn13.setChecked(true);
    }

    CompoundButton.OnCheckedChangeListener changeChecker = new CompoundButton.OnCheckedChangeListener() {
        @Override
        public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
            if (isChecked) {
                if (buttonView == one) {
                    two.setChecked(false);
                    three.setChecked(false);
                    four.setChecked(false);
                    five.setChecked(false);
                    six.setChecked(false);
                     a = 74.43;
                     SummaA(a);
                }
                if (buttonView == two) {
                    one.setChecked(false);
                    three.setChecked(false);
                    four.setChecked(false);
                    five.setChecked(false);
                    six.setChecked(false);
                    a = 152.86;
                    SummaA(a);

                }
                if (buttonView == three) {
                    two.setChecked(false);
                    one.setChecked(false);
                    four.setChecked(false);
                    five.setChecked(false);
                    six.setChecked(false);
                    a = 380.13;
                    SummaA(a);
                }
                if (buttonView == four) {
                    two.setChecked(false);
                    three.setChecked(false);
                    one.setChecked(false);
                    five.setChecked(false);
                    six.setChecked(false);
                    a = 580.13;
                    SummaA(a);
                }
                if (buttonView == five) {
                    two.setChecked(false);
                    three.setChecked(false);
                    one.setChecked(false);
                    four.setChecked(false);
                    six.setChecked(false);
                    a = 880.13;
                    SummaA(a);
                }
                if (buttonView == six) {
                    two.setChecked(false);
                    three.setChecked(false);
                    one.setChecked(false);
                    five.setChecked(false);
                    four.setChecked(false);
                    a = 1380.13;
                    SummaA(a);
                }
            }
        }
        
    };
        CompoundButton.OnCheckedChangeListener changeChecker3 = new CompoundButton.OnCheckedChangeListener() {
        @Override
        public void onCheckedChanged(CompoundButton buttonView3, boolean isChecked) {
            if (isChecked) {
                if (buttonView3 == btn13) {
                    btn14.setChecked(false);
                    btn15.setChecked(false);
                    d = 119.87;
                    SummaD(d);
                }
                if (buttonView3 == btn14) {
                    btn13.setChecked(false);
                    btn15.setChecked(false);
                    d = 265.59;
                    SummaD(d);
                }
                if (buttonView3 == btn15) {
                    btn13.setChecked(false);
                    btn14.setChecked(false);
                    d = 411.31;
                    SummaD(d);
                }
            }
        }
    };
}