how do i do a calculation on a windows application

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
namespace q3
{
    public partial class Form1 : Form
    {
        int bpd;
        int bpw;
        int bpm;
        int bpy;
        int bted;
        int enb;
        public Form1()
        {
            InitializeComponent();
        }
        private void btnenter_Click(object sender, EventArgs e)
        {
            bpd = 70 * 23;
            bpw = 1680 * 5;
            bpm = 11760 * 6;
            bpy = 47040 * 13;
            bted = 564480 * 39;
            enb = 22456560 + 16800;

        }

        private void txtheartbeats_TextChanged(object sender, EventArgs e)
        {
            txtheartbeats.Text = "enb";
        }
        private void txtname_TextChanged(object sender, EventArgs e)
        {
            txtname.Text = "John Smith";
        }
        private void txtDob_TextChanged(object sender, EventArgs e)
        {
            txtDob.Text = "05/10/1990";
        }
        private void txtTargetdate_TextChanged(object sender, EventArgs e)
        {
            txtTargetdate.Text = "11/10/2020";
        }

    }
}