Check this below XML, just for the reference. You need to change somethings like ImageButton to Button etc, but it will solve your problem.
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<LinearLayout
android:layout_width="fill_parent"
android:layout_height="60dp"
android:background="#ffff" >
<LinearLayout
android:layout_width="match_parent"
android:layout_height="60dp" >
<LinearLayout
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="1"
android:gravity="center" >
<ImageButton
android:id="@+id/image_agenda"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:adjustViewBounds="true"
android:src="@drawable/ic_launcher" />
</LinearLayout>
<LinearLayout
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="1"
android:gravity="center" >
<ImageButton
android:id="@+id/image_month"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:adjustViewBounds="true"
android:src="@drawable/ic_launcher" />
</LinearLayout>
<LinearLayout
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="1"
android:gravity="center" >
<ImageButton
android:id="@+id/image_day"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:adjustViewBounds="true"
android:src="@drawable/ic_launcher" />
</LinearLayout>
</LinearLayout>
</LinearLayout>