how to give the textbox value in text as 14.5/100 as default

Question

how to give the textbox value in text as 14.5/100 as default

in textbox i  use default value as (14.5/100) i never give the value in run time 

i need to multiply the value with next textbox . given  value in  source code .

need to multiply the default value in source code 

my design is 

    <table class="style1">

        <tr>

            <td>

                a</td>

            <td>

                <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>

            </td>

        </tr>

        <tr>

            <td>

                b</td>

            <td>

                <asp:TextBox ID="TextBox2" runat="server" ontextchanged="TextBox2_TextChanged" AutoPostBack="true"></asp:TextBox>

            </td>

        </tr>

        <tr>

            <td>

                a+b</td>

            <td>

                <asp:TextBox ID="TextBox3" runat="server"></asp:TextBox>

            </td>

        </tr>

        <tr>

            <td>

                mul</td>

            <td>

                <asp:TextBox ID="TextBox4" runat="server" ontextchanged="TextBox4_TextChanged" 

                    AutoPostBack="True"></asp:TextBox>

            </td>

        </tr>

        <tr>

            <td>

                multl</td>

            <td>

                <asp:TextBox ID="TextBox5" runat="server"></asp:TextBox>

            </td>

        </tr>

</table>

my coding is 

using System;

using System.Collections;

using System.Configuration;

using System.Data;

using System.Linq;

using System.Web;

using System.Web.Security;

using System.Web.UI;

using System.Web.UI.HtmlControls;

using System.Web.UI.WebControls;

using System.Web.UI.WebControls.WebParts;

using System.Xml.Linq;

using System.Data.SqlClient;

public partial class math : System.Web.UI.Page

{

    REMO sel = new REMO();

    protected void Page_Load(object sender, EventArgs e)

    {

    }

    protected void Button1_Click(object sender, EventArgs e)

    {

        

      

       // float c= float.Parse(TextBox1.Text) + float.Parse(TextBox2.Text);

       //TextBox3.Text = Convert.ToString(c);

        //float s = c * float.Parse(TextBox4.Text);

        //float s = ((c * float.Parse(TextBox4.Text)));

        //TextBox5.Text = Convert.ToString(s);

       

      

    }

    protected void TextBox4_TextChanged(object sender, EventArgs e)

    {

        double guna = int.Parse(TextBox3.Text) * (14.5 / 100);

        TextBox5.Text = Convert.ToString(guna);

       

        

    }

    protected void TextBox2_TextChanged(object sender, EventArgs e)

    {

        float c = float.Parse(TextBox1.Text) + float.Parse(TextBox2.Text);

        TextBox3.Text = Convert.ToString(c);

    }

}

textbox3* textbox4 as default value (14.5/100) =textbox5

in run time i given the value as 14.5/100 my coding is working but. i need textbox4 value as default text as 14.5/100 used in source code. multiply with textbox3. and need to show the output in textbox5