C# how to multiply combobox and textbox

private void button1_Click(object sender, EventArgs e)
        {
            int x = 0;
            string p1 = txt1.SelectedItem.ToString();//Combobox
            if(p1 == "HTML/CSS")
            {
                x += 4200;
            }
            else if(p1 == "Photoshop/Illustrator")
            {
                x += 4000;
            }
            else
            {
                x += 3500;
            }
            string p2 = txt2.SelectedItem.ToString();//Combobox
            if(p2 == "JavaScript")
            {
                x += 5700;
            }
            else if(p2 == "PHP")
            {
                x += 6000;
            }
            else if(p2 == "Java")
            {
                x += 5000;
            }
            else
            {
                x += 4500;
            }
            string p3 = txt3.SelectedItem.ToString();//Combobox
            if(p3 == "Ալգորիթմների տեսություն")
            {
                x += 12500;
            }
            else
            {
                x += 15000;
            }
            string y = txt4.Text; //Textbox
            int z = y * (p1 + p2 + p3)

        }