how to merge two apps in adroid java

i have the .xml and .java files of both apps. i want to crete a row of buttons on the left handside that on a click of a button it will take u to some other page.

this is the xml file of app1.

<RelativeLayout xmlns:android="http://ift.tt/nIICcg"
xmlns:tools="http://ift.tt/LrGmb4"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".MainActivitywhatsyourgrade" >

<TextView
    android:id="@+id/textView1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentTop="true"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="22dp"
    android:text="Type in your marks" />

<EditText
    android:id="@+id/testscore"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentLeft="true"
    android:layout_alignParentRight="true"
    android:layout_below="@+id/textView1"
    android:ems="10" >

    <requestFocus />
</EditText>

<EditText
    android:id="@+id/editText2"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@+id/button1"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="106dp"
    android:ems="10" />

<Button
    android:id="@+id/button1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@+id/testscore"``
    android:layout_centerHorizontal="true"
    android:layout_marginTop="68dp"
    android:text="what&apos;s my grade" />

and this is the .java file of app1

public class MainActivitywhatsyourgrade extends Activity {
protected static final int A = 0;
Button bt1;
EditText etxt1;
EditText etxt2;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main_activitywhatsyourgrade);
    bt1=(Button)findViewById(R.id.button1);
    etxt1=(EditText)findViewById(R.id.testscore);
    etxt2=(EditText)findViewById(R.id.editText2);
    bt1.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View arg0) {
            // TODO Auto-generated method stub
            String strScore = etxt1.getText().toString();
            int score = Integer.parseInt(strScore);
            if (score >=90){
                etxt2.setText("A1");
            }
            else if(score>=80){
                etxt2.setText("A2");
            }
            else if(score>=70){
                etxt2.setText("B1");
            }
            else if(score>=60){
                etxt2.setText("B2");
            }
            else if (score>=50){
                etxt2.setText("C1");
            }
            else if (score>=40){
                etxt2.setText("C2");
            }
            else if (score>=32){
                etxt2.setText("D");
            }
            else if (score>=20){
                etxt2.setText("E1");
            }
            else if (score>=-1){
                etxt2.setText("E2");
            }

        }
    });

}



@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main_activitywhatsyourgrade, menu);
    return true;


}

}

the second .xml and .java files are the same. just that one is for calss 9 and the other is for calss 10. i want create a list of button on the left handside to take me where i want ether the calss9 xml or class 10 xml.