Does this help?
Private Sub TXTnumbers_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TXTnumber1.TextChanged, TXTnumber2.TextChanged, TXTnumber3.TextChanged, TXTnumber4.TextChanged, TXTnumber5.TextChanged
Dim txtnumbers() As TextBox = {TXTnumber1...