How to get records from different tables using webservices

Question

Here is my Database diagram and my scenario is that When a user enter number of person and amount, amount/person
let suppose 4/1000=250 and now 250 is , match in Product_Price Field in RstProductDetails, and select only Restaurant where 250 is matched. Next when a user select Restaurant e.g KFC and then KFC Products details is show.
Here is my [WebMethod]

 [WebMethod]

    public DataSet Restaurant(string amount, string persons)

    {

        //        DataSet result = Amount / personHash;

         decimal price = amount \ persons ;

        DataSet result = null;

        const string SQL_COMMAND_TEXT = "SELECT Rst_Name FROM RstProductDetails WHERE Product_Price WHERE Product_rice< = @price";

        using (SqlConnection connection = Class1.GetConnection())

        {

            connection.Open();

            using (SqlCommand command = new SqlCommand(SQL_COMMAND_TEXT, connection))

            {

                command.Parameters.Add("@Rst_Name", SqlDbType.NVarChar);

                command.Parameters.Add("@PersonHash", SqlDbType.NVarChar);

                command.Parameters.Add("@price", SqlDbType.Decimal);

                command.Parameters["@Rst_Name"].Value = amount;

                command.Parameters["@persons"].Value = persons;

                command.Parameters["@price"].Value = price;

                using (SqlDataAdapter dataAdapter = new SqlDataAdapter(command))

                {

                    result = new DataSet();

                    dataAdapter.Fill(result);

                }

            }

        }

        return result;

    }

Here is my databse relation diagram