ошибка AAPT: error: attribute android:hintTextColor not found

Надо сделать простейший калькулятор, но не связывает элементы и вылезает следующая ошибка AAPT: error: attribute android:hintTextColor not found.

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#fafafa"
    tools:context=".MainActivity">

    <EditText
        android:id="@+id/Num1"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:layout_marginStart="1dp"
        android:layout_marginTop="84dp"
        android:layout_marginEnd="1dp"
        android:layout_marginBottom="20dp"
        android:ems="10"
        android:hint="Первое число"
        android:hintTextColor="#000000"
        android:inputType="number"
        android:textColor="#546E7A"
        app:layout_constraintBottom_toTopOf="@+id/Num2"
        app:layout_constraintEnd_toEndOf="@+id/Num2"
        app:layout_constraintStart_toStartOf="@+id/Num2"
        app:layout_constraintTop_toTopOf="parent" />

    <EditText
        android:id="@+id/Num2"
        android:layout_width="215dp"
        android:layout_height="0dp"
        android:layout_marginStart="20dp"
        android:layout_marginBottom="56dp"
        android:ems="10"
        android:hint="Второе число"
        android:hintTextColor="#000000"
        android:inputType="number"
        android:minHeight="48dp"
        android:textColor="#546E7A"
        app:layout_constraintBottom_toTopOf="@+id/Result"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/Num1" />

    <TextView
        android:id="@+id/Result"
        android:layout_width="105dp"
        android:layout_height="0dp"
        android:layout_marginEnd="98dp"
        android:layout_marginBottom="7dp"
        android:text="Результат"
        android:hintTextColor="#000000"
        android:textColor="#546E7A"
        android:textSize="20sp"
        app:layout_constraintBottom_toTopOf="@+id/sum"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/Num2" />

    <Button
        android:id="@+id/sum"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="36dp"
        android:layout_marginBottom="365dp"
        android:text="+"
        android:hintTextColor="#000000"
        android:textColor="#546E7A"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/Result" />
</android.support.constraint.ConstraintLayout>

и

package com.example.nfpapp;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
    public void onButtonClick (View v) {
        EditText el1 = (EditText) findViewById(R.id.Num1);
        EditText el2 = (EditText) findViewById(R.id.Num2);
        TextView resText =  (TextView) findViewById(R.id.Result);
        int num1 = Integer.parseInt(el1.getText().toString());
        int num2 = Integer.parseInt(el2.getText().toString());
        int resSum = num1 + num2;
        resText.setText(Integer.toString(resSum));
    }
}