app error

hi! I try to make an easy app which display sum of 2 number but when i run the app in the virtual manager i receive this error ( first image) why?

 

Code (Text):

1.  
2. <?xml version="1.0" encoding="utf-8"?>
3. <android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
4.     xmlns:app="http://schemas.android.com/apk/res-auto"
5.     xmlns:tools="http://schemas.android.com/tools"
6.     android:layout_width="match_parent"
7.     android:layout_height="match_parent"
8.     tools:context="com.example.slimjr.proiectf.MainActivity"
9.     tools:layout_editor_absoluteY="81dp"
10.     tools:layout_editor_absoluteX="0dp">
11.  
12.     <EditText
13.         android:id="@+id/txt1"
14.         android:layout_width="wrap_content"
15.         android:layout_height="wrap_content"
16.         android:ems="10"
17.         android:hint="X"
18.         android:inputType="number"
19.         app:layout_constraintLeft_toLeftOf="parent"
20.         app:layout_constraintRight_toRightOf="parent"
21.         tools:layout_editor_absoluteY="46dp" />
22.  
23.     <EditText
24.         android:id="@+id/txt2"
25.         android:layout_width="wrap_content"
26.         android:layout_height="wrap_content"
27.         android:ems="10"
28.         android:hint="Y"
29.         android:inputType="number"
30.         tools:layout_editor_absoluteX="85dp"
31.         tools:layout_editor_absoluteY="108dp" />
32.  
33.     <Button
34.         android:id="@+id/button"
35.         android:layout_width="wrap_content"
36.         android:layout_height="wrap_content"
37.         android:eek:nClick="onButtonClick"
38.         android:text="Suma"
39.         tools:layout_editor_absoluteX="148dp"
40.         tools:layout_editor_absoluteY="218dp" />
41.  
42.     <TextView
43.         android:id="@+id/res"
44.         android:layout_width="75dp"
45.         android:layout_height="42dp"
46.         android:text="rezultat"
47.         tools:layout_editor_absoluteX="154dp"
48.         tools:layout_editor_absoluteY="168dp" />
49.  
50. </android.support.constraint.ConstraintLayout>
51.  

 

i made it . i used relative layout in xml. this is my first app
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"