How to get SubTotal based on Quantity and Price Using asp.net & C#

See more:

C#

ASP.NET

C#4.0

public void SalePrice()
    {
        double originalPrice, discountPercentage, discountAmount, salePrice;
        con.Open();
        SqlCommand sqlcom = new SqlCommand("USP_SalePriceCalculation", con);
        sqlcom.CommandType = CommandType.StoredProcedure;
        SqlDataAdapter da = new SqlDataAdapter(sqlcom);
        DataTable dt = new DataTable();
        da.Fill(dt);
        if (dt.Rows.Count > 0)
        {
            // Get item's original price.
            originalPrice = double.Parse(dt.Rows[0]["actprice"].ToString());

            // Get discount percentage.
            discountPercentage = double.Parse(dt.Rows[0]["Discount"].ToString());

            // Create decimal representation of %  (move point left two places)
            discountPercentage = discountPercentage / 100;

            // Calculate amount of the discount.
            discountAmount = originalPrice * discountPercentage;

            // Calculate sale price.
            salePrice = originalPrice - discountAmount;

            // Display sale price as Currency ("c")
            lblPrice.Text = salePrice.ToString("c", Cultures.INDIA);
        }
        con.Close();        
    }
    public static class Cultures
    {
        public static readonly CultureInfo INDIA =
            CultureInfo.GetCultureInfo("en-IN");
    }

Now i want to Calcualate SubTotal Based on that SalePrice and Quantity(textbox)
Any one help me that how to calculate SubTotal?