Whole project is in here:

https://github.com/LEOHAPPY/ASP.NET-Sample-Paper

WebForm1.aspx.cs

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class WebForm1 : System.Web.UI.Page
{
    static ArrayList receipts = new ArrayList();
    string vehicle;
    protected void Page_Load(object sender, EventArgs e)
    {
        vehicle = tb_vn.Text.ToString();
        
        //clear history in the receipts when first load in this page 
        if (!IsPostBack)
        {
            receipts.Clear();
        }
    }

    protected void add_btn_Click(object sender, EventArgs e)
    {
        //Bind to GridView1
        Receipt r = new Receipt();
        r.Shop = tb_receipt.Text.ToString();
        r.Receipt_sn = tb_sn.Text.ToString();
        r.Amount = Convert.ToDouble(tb_amount.Text.ToString());
        receipts.Add(r);

        GridView1.DataSource = receipts;
        GridView1.DataBind();

        //get dataset
        dsVehicleRb ds = new dsVehicleRb();
        dsVehicleRbTableAdapters.vehicleRbTableAdapter ad =
            new dsVehicleRbTableAdapters.vehicleRbTableAdapter();
        ad.Fill(ds.vehicleRb);

        //update existingDebate
        for (int i = 0; i < ds.vehicleRb.Count; i++)
        {
            if (vehicle == ds.vehicleRb.Rows[i][0].ToString())
            {
                ds.vehicleRb.Rows[i][1] =
                    Convert.ToDouble(ds.vehicleRb.Rows[i][1].ToString()) + r.Amount;
                ad.Update(ds.vehicleRb);
                break;
            }
        }

        //refresh existingRebate textbox
        tb_er.Text = findExistingRebate().ToString();
        tb_rt.Text = null;
    }

    protected void btn_apply_Click(object sender, EventArgs e)
    {
        //calculate current rebate tickets
        int currentRebateTickets = applyRebates(vehicle, receipts);
        //dispaly on the rebate tickets textbox
        tb_rt.Text = currentRebateTickets.ToString();

        //refresh exiting rebate
        tb_er.Text = findExistingRebate().ToString();

        //refresh list and gridview
        applyRefresh(currentRebateTickets);
    }

    public void applyRefresh(int currentRebateTickets)
    {
        if (currentRebateTickets != 0)
        {
            receipts.Clear();
            GridView1.DataSource = receipts;
            GridView1.DataBind();

            tb_receipt.Text = null;
            tb_sn.Text = null;
            tb_amount.Text = null;
        }
       
    }
    
    public int applyRebates(string vehicle, ArrayList receipts)
    {
        //logic: ? hour car-parking is credited to the shopper’s vehicle for every $25 spent on shopping accumulated in shopping receipts
        double appliedRebates = 0.0;
        //get existingRebate
        double exitingRebate = findExistingRebate();

        //calculate rebate tickets 
        int currentRebateTickets = Convert.ToInt16(Math.Floor(exitingRebate / 25));

        //apply to database
        //get dataset
        dsVehicleRb ds = new dsVehicleRb();
        dsVehicleRbTableAdapters.vehicleRbTableAdapter ad =
            new dsVehicleRbTableAdapters.vehicleRbTableAdapter();
        ad.Fill(ds.vehicleRb);

        //update existingDebate
        for (int i = 0; i < ds.vehicleRb.Count; i++)
        {
            if (vehicle == ds.vehicleRb.Rows[i][0].ToString())
            {
                appliedRebates = exitingRebate - currentRebateTickets * 25;
                ds.vehicleRb.Rows[i][1] = appliedRebates;
                ad.Update(ds.vehicleRb);
                break;
            }
        }
        return currentRebateTickets;
    }

    public dsVehicleRb useDataset()
    {
        //fill dataset
        dsVehicleRb ds = new dsVehicleRb();
        dsVehicleRbTableAdapters.vehicleRbTableAdapter ad =
            new dsVehicleRbTableAdapters.vehicleRbTableAdapter();
        ad.Fill(ds.vehicleRb);
        return ds;
    }
    protected void bt_find_Click(object sender, EventArgs e)
    {
        tb_er.Text = findExistingRebate().ToString();
    }

    public double findExistingRebate()
    {
        dsVehicleRb ds = useDataset();

        //find and return
        double existingRebate = 0.0;
        for (int i = 0; i < ds.vehicleRb.Count; i++)
        {
            if (vehicle == ds.vehicleRb.Rows[i][0].ToString())
            {
                existingRebate = (double)ds.vehicleRb.Rows[i][1];
                break;
            }
        }
        return existingRebate;

        //another way to find
        // var q = ds.vehicleRb.Where(x => x.vehicleNum == vehicle).ToList();
        ////double stingRb= q.Select(y => y.existingRebates);
        //GridView2.DataSource = q;
        //GridView2.DataBind();
    }
}

Picture of webForm1

Pic_WebForm1.jpeg

WebForm1.aspx

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="WebForm1.aspx.cs" Inherits="WebForm1" %>

<!DOCTYPE html>

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
    
        <asp:Label ID="Label1" runat="server" Text="Parking Rebate system"></asp:Label>
        <br />
        <asp:Label ID="Label2" runat="server" Text="Vehicle number:"></asp:Label>
        <asp:TextBox ID="tb_vn" runat="server"></asp:TextBox>
        <br />
        <br />
        <asp:Label ID="Label3" runat="server" Text="Parking Rebate system"></asp:Label>
        <br />
        <asp:Label runat="server" Text="Receipt s/n : "></asp:Label>
        <asp:TextBox ID="tb_receipt" runat="server"></asp:TextBox>
        <br />
        <asp:Label ID="Label5" runat="server" Text="Shop name : "></asp:Label>
        <asp:TextBox ID="tb_sn" runat="server"></asp:TextBox>
        <br />
        <asp:Label ID="Label6" runat="server" Text="Amount :     "></asp:Label>
        <asp:TextBox ID="tb_amount" runat="server"></asp:TextBox>
        <br />
        <asp:Button ID="btn_add" runat="server" OnClick="add_btn_Click" Text="Add Receipt" />
        <br />
        
        
        <asp:GridView ID="GridView1" runat="server">
        </asp:GridView>
        <br />
        <br />
        <asp:Button ID="btn_apply" runat="server" Text="Apply Rebates" OnClick="btn_apply_Click" />
    
        <br />
        <asp:Label runat="server" Text="Rebate Tickets : " ID="Label7"></asp:Label>
        <asp:TextBox ID="tb_rt" runat="server"></asp:TextBox>
        <br />
        <br />
        <asp:Button ID="bt_find" runat="server" OnClick="bt_find_Click" Text="Find Exsiting  Rebates" />
        <br />
        <asp:Label runat="server" Text="Existing Rebates : " ID="Label8"></asp:Label>
        <asp:TextBox ID="tb_er" runat="server"></asp:TextBox>
    
        <br />
    
    </div>
    </form>
</body>
</html>