adding admobs on my android app - android-layout

Question

Please assist with something,I am trying to add admobs on the app but it doesn't show on the app when I run it, but it appears on the android studio preview. How do I fix that?
This code is on the main activity layout
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:ads="http://schemas.android.com/apk/res-auto"
android:id="#+id/relatively"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#d15400"
android:orientation="vertical"
android:weightSum="1" >
<LinearLayout
android:id="#+id/linearLayout1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="0.90"
android:orientation="vertical"
android:weightSum="1" >
<LinearLayout
android:id="#+id/linearLayout11"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="0.20"
android:orientation="vertical"
android:weightSum="1" >
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="1"
android:orientation="horizontal" >
<TextView
android:id="#+id/score"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:layout_gravity="center"
android:layout_marginRight="10dp"
android:layout_weight="1"
android:gravity="center"
android:text="Score : 1"
android:textColor="#ffffff"
android:textSize="25.0sp"
android:textStyle="bold" />
<TextView
android:id="#+id/timers"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:layout_gravity="center"
android:layout_marginRight="10dp"
android:layout_weight="1"
android:gravity="center"
android:text="00:00:49"
android:textColor="#ffffff"
android:textSize="25.0sp"
android:textStyle="bold" />
</LinearLayout>
</LinearLayout>
<LinearLayout
android:id="#+id/linearLayout12"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="0.60"
android:orientation="vertical"
android:weightSum="1" >
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="0.40" >
<TextView
android:id="#+id/txtQuestion"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:layout_gravity="center"
android:layout_marginTop="5dp"
android:gravity="center"
android:text="15*2*1-1"
android:textColor="#ffffff"
android:textSize="35.0sp"
android:textStyle="bold" />
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="0.20"
android:orientation="vertical"
android:weightSum="1" >
<Button
android:id="#+id/button1"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:layout_marginLeft="80dp"
android:layout_marginRight="80dp"
android:layout_marginTop="5dp"
android:background="#fff"
android:gravity="center"
android:text="30"
android:textColor="#000000"
android:textSize="25.0sp" />
<Button
android:id="#+id/button2"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:layout_marginLeft="80dp"
android:layout_marginRight="80dp"
android:layout_marginTop="5dp"
android:background="#fff"
android:gravity="center"
android:text="29"
android:textColor="#000000"
android:textSize="25.0sp" />
<Button
android:id="#+id/button3"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:layout_marginLeft="80dp"
android:layout_marginRight="80dp"
android:layout_marginTop="5dp"
android:background="#fff"
android:gravity="center"
android:text="32"
android:textColor="#000000"
android:textSize="25.0sp" />
<!-- view for AdMob Banner Ad -->
</LinearLayout>
</LinearLayout>
</LinearLayout>
<com.google.android.gms.ads.AdView
android:id="#+id/adView"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:layout_alignParentBottom="true"
ads:adSize="BANNER"
ads:adUnitId="#string/banner_ad_unit_id">
</com.google.android.gms.ads.AdView>
</LinearLayout>
this code is on the questions activity class -
setContentView(R.layout.activity_main);
AdView adView = (AdView) findViewById(R.id.adView);
AdRequest adRequest = new AdRequest.Builder()
.setRequestAgent("android_studio:ad_template").build();
adView.loadAd(adRequest);