Reference to a non-shared member...

[jhaag4]

So in my class we have an assignment to create a cash register. I got it to work fine originally but the assignment calls for a class called CashRegister(which I have never done before), a property called Balance, and add method and a subtract method. So I tried to do that but now all my text boxes, when I reference them, are giving me the error "reference to a nonshared member..". HOw do i fix this? My code is:

Public Class frmRegister
    Private Sub frmRegister_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        If txtBalance.Text = "" Then
            txtBalance.Text = "0"
        End If
    End Sub
    Class CashRegister
        Private Balance As Integer
        Private addAmount As Double
        Private subAmount As Double
        Public Property AddMethod As Double
            Get
                Return addAmount
            End Get
            Set(ByVal value As Double)
                Dim x As Integer = Val(txtAmount.Text)
                Dim y As Integer = Val(txtBalance.Text)
                addAmount = x + y
            End Set
        End Property
        Public Property SubtractMethod As Double
            Get
                Return subAmount
            End Get
            Set(ByVal value As Double)
                Dim x As Integer = Val(txtAmount.Text)
                Dim y As Integer = Val(txtBalance.Text)
                subAmount = y - x
            End Set
        End Property

        Private Sub btnAdd_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAdd.Click
            txtBalance.Text = FormatCurrency(addAmount)
        End Sub

        Private Sub btnSubtract_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSubtract.Click
          
            txtBalance.Text = FormatCurrency(subAmount)
            If txtBalance.Text < 0 Then
                MessageBox.Show("Transaction Cannot Result in Negative Balance!")
                txtBalance.Text = "0"
            End If

        End Sub

    End Class
End Class

ANy help would be appreciated?