Суммирование значений EditText в textWatcher Android

У меня есть RecyclerView в котором создаются динамично поля.Для сохранения ведённых данных я использовал textWatcher.Но я не знаю как мне суммировать значения которые находятся в EditText -Cost и вывести значение в TextView в низу экрана

public class ItemsAdapter extends ListAdapter { private List mItems=new ArrayList<>();

    public static final DiffUtil.ItemCallback<Item>DIFF_CALLBACK=
            new DiffUtil.ItemCallback<Item>() {
                @Override
                public boolean areItemsTheSame( Item oldItem, Item newItem) {
                    return oldItem.getId()==newItem.getId();
                }
                @Override
                public boolean areContentsTheSame(Item oldItem, Item newItem) {
                    return(oldItem.getName()==newItem.getName()&&oldItem.getCost()==newItem.getCost());
                }
            };
    public ItemsAdapter(){super(DIFF_CALLBACK);}
    public void addMorreItems(List<Item> newItems){
        int insertionPosition=mItems.size();
        mItems.addAll(newItems);
        notifyItemRangeInserted(insertionPosition,newItems.size());
        submitList(mItems);
    }
    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType){
        Context context=parent.getContext();
        LayoutInflater inflater=LayoutInflater.from(context);
        View itemView=inflater.inflate(R.layout.custom_edittext_layout,parent,false);
        ViewHolder viewHolder=new ViewHolder(itemView);
        return viewHolder;
    }
    @Override
    public void onBindViewHolder(ViewHolder viewHolder,int position){
        viewHolder.editTextName.setText(mItems.get(position).getName());
        viewHolder.editTextCost3.setText(mItems.get(position).getCost());
        Item item=getItem(position);
        EditText editText=viewHolder.editTextName;
        editText.setText(item.getName());
        EditText editText1=viewHolder.editTextCost3;
        editText1.setText(item.getCost());
    }

    public class ViewHolder extends RecyclerView.ViewHolder {
        public EditText editTextName;
        public EditText editTextCost3;
        public TextView txtTipAmount3;
        public Button buttonDelete;
        public  Button buttonOK;
        public ViewHolder(View itemView){
            super(itemView);
            editTextCost3=(EditText)itemView.findViewById(R.id.ediCost3);
            editTextName=(EditText)itemView.findViewById(R.id.editTextEnterYourName);
            txtTipAmount3=(TextView)itemView.findViewById(R.id.txtTipAmount3);
            buttonDelete=(Button)itemView.findViewById(R.id.buttonDelete);
            buttonOK=(Button)itemView.findViewById(R.id.buttonOk);
            buttonDelete.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    int position=getAdapterPosition();
                    try {
                        mItems.remove(position);
                        notifyItemRemoved(position);
                    }catch (ArrayIndexOutOfBoundsException e){e.printStackTrace();}
                }
            });
            editTextName.addTextChangedListener(new TextWatcher() {
                @Override
                public void beforeTextChanged(CharSequence s, int start, int count, int after) {
                }
                @Override
                public void onTextChanged(CharSequence s, int start, int before, int count) {
                    mItems.get(getAdapterPosition()).setmName(editTextName.getText().toString());
                }
                @Override
                public void afterTextChanged(Editable s) {
                }
            });
            editTextCost3.addTextChangedListener(new TextWatcher() {
                @Override
                public void beforeTextChanged(CharSequence s, int start, int count, int after) {
                }
                @Override
                public void onTextChanged(CharSequence s, int start, int before, int count) {
                    mItems.get(getAdapterPosition()).setmCost(editTextCost3.getText().toString());
                }
                @Override
                public void afterTextChanged(Editable s) {
                }
            });
        }
    } }