use a RelativeLayout or wrap the ImageView in a LinearLayout :
---- EDIT ----
on the ImageView : take out the layout_gravity and margin_top attributes and set layout_height to 0dp
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal"
android:weightSum="100" >
<TextView
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="20" />
<LinearLayout
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="60"
android:orientation="vertical"
android:weightSum="100" >
<TextView
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="30" />
<ImageView
android:id="@+id/imageView4"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="40"
android:src="@drawable/logo_line" />
</LinearLayout>
<TextView
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="20" />
</LinearLayout>