Keeping Track of Totals in Visual Basic - vb.net

Question

I am trying to code an application that will keep track of the total amount of cars sold through the person's ID number. I have coded it so that the car totals show in their respective fields but how do I get it so that the totals are saved after I input more ID numbers. The below is the ID requirements.
The first number can be either 1 or 2. 1 is new cars sold while 2 is used cars sold.
The last letter of the ID is P (Part time) or F (Full Time).
The setup is like this:
ID: Number of cars sold:
(Textbox to input ID#) (Textbox to input number of cars sold)
Calculate Button Exit Button
Total of cars sold by full-time employees: (label to display total)
Total of cars sold by part-time employees: (label to display total)
Total of new cars sold: (label to display total)
Total of used cars sold: (label to display total)
Here's my code. I want to keep a running total for each depending on the input ID number. So if I put it 1MBP sold 7 cars and 1DKP sold 7 cars, the totals for new cars and part-time employee should show 14
' Name: Huntington Motors Sales Application
' Purpose: The application will calculate the number and type of cars sold as per
' input from the manager. The ID number specifies the type of sales person
' sold the car which is how the application will calculate the total.
' Programmer: Marlinda Davis on October 15, 2015
Option Explicit On
Option Strict On
Option Infer Off
Public Class frmMain
Private Sub btnCalc_Click(sender As Object, e As EventArgs) Handles btnCalc.Click
Dim strId As String
Dim intNumSold As Integer
Dim intNew As Integer
Dim intUsed As Integer
Dim intPartTime As Integer
Dim intFullTime As Integer
' identify characters in ID '
strId = txtIDNum.Text.Trim.ToUpper
Integer.TryParse(txtNumSold.Text, intNumSold)
' verify that the ID contains a number followed by 3 numbers
' The first number 1 = new car sales person or 2 = used car sales person
' The next two letters are the person's initials
' The last letter indicates if the person is full time(F) or part time(P)
If strId Like "[12][A-Z][A-Z][FP]" Then
If strId.Substring(0) = "1" Then
intNew = intNew + intNumSold
lblNewNum.Text = intNew.ToString
Else
intUsed = intUsed + intNumSold
lblUsedNum.Text = intUsed.ToString
End If
If strId.Substring(3) = "F" Then
intFullTime = intFullTime + intNumSold
lblFTNum.Text = intFullTime.ToString
Else
intPartTime = intPartTime + intNumSold
lblPTNum.Text = intPartTime.ToString
End If
End If
' refocus on ID input box after each entry '
txtIDNum.Focus()
txtIDNum.SelectAll()
End Sub
Private Sub btnExit_Click(sender As Object, e As EventArgs) Handles btnExit.Click
Me.Close()
End Sub
Private Sub frmMain_FormClosing(sender As Object, e As FormClosingEventArgs) Handles Me.FormClosing
Const strEXIT As String = "Are you sure you want to close this application?"
Dim dlgExit As DialogResult
' verify the user wants to close the application '
dlgExit = MessageBox.Show(strEXIT, "Huntington Motors", MessageBoxButtons.YesNo,
MessageBoxIcon.Exclamation)
' if the user answers No then the application will not close '
If dlgExit = System.Windows.Forms.DialogResult.No Then
e.Cancel = True
End If
End Sub
End Class