how to keep value when clicking on button in a form?

Hi

there are 2 times two textbox for entering two numbers and two times a button to make the sum of them.

When i click on the second button for making the sum of the 3th and 4th textbox, the sum of the first and second textbox disappears.

How can i keep the first sum visible while i click on the second button? I tried with EnableViewState="true" but no succes.

Thanks.

V

My code:

 protected void Button1_Click(object sender, EventArgs e)
    {       
        if (int.TryParse(TextBox1.Text, out g1) && int.TryParse(TextBox2.Text, out g2))
        {
            int sum = g1 + g2;
            Label4.Text = sum.ToString();
        }

protected void Button2_Click(object sender, EventArgs e)
    {
        if (int.TryParse(TextBox3.Text, out g1) && int.TryParse(TextBox4.Text, out g2))
        {
            int sum = g1 + g2;
            Label7.Text = sum.ToString();
        }
     }
}