Вычислить сумму целых положительных чисел, больших М, меньших N и кратных K

Option Explicit
 
Const s = "7 5 9 1 3 5", s1 = "Задумай число, " & vbLf & "и нажми далее"
Dim oper&, oldt$
Dim lb As Label, WithEvents tx As TextBox, WithEvents cb1 As CommandButton, WithEvents cb2 As CommandButton, l&, t&, w&, h&
 
Dim ob(5) As OptionButton, i&, j$()
 
 
Const r = 90
 
Private Sub cb1_Click()
    oldt = tx
    Select Case oper
    Case 0
        lb.Caption = "Теперь добавьте к этому числу, одно из:"
        For i = 0 To UBound(ob)
            ob(i).Visible = 1
        Next
        cb1.Width = w / 2
        cb2.Left = cb1.Left + cb1.Width + r
        cb2.Visible = 1
        
    Case 1:  For i = 0 To UBound(ob): Do While ob(i): Exit For: Exit Do: Loop: Next: tx = CLng(tx) + CLng(j(i))
        For i = 0 To UBound(ob): ob(i).Visible = 0: Next
        lb.Caption = "Теперь нужно прибавить 9" & vbLf & " и разделить на 2"
        Stop
    Case Else
End Select
oper = oper + 1
End Sub
 
Private Sub cb2_Click()
    oper = oper - 1
    Select Case oper
    Case 0
        cb1.Width = w
        cb2.Visible = 0
        For i = 0 To UBound(ob): ob(i).Visible = 0: Next
        lb.Caption = s1
         tx = oldt
    Case 1
         tx = oldt
    Case 2
    Case 3
    End Select
    
End Sub
 
Private Sub tx_Change()
    Do Until IsNumeric(tx): tx = 0: tx.SelStart = 0: tx.SelLength = 2 ^ 8: Exit Do: Loop
End Sub
 
Private Sub tx_KeyPress(KeyAscii As Integer): Do Until KeyAscii = 8 Or KeyAscii > 47 And KeyAscii < 58: KeyAscii = 0: Exit Do: Loop: End Sub
 
Private Sub Form_Load()
    l = r: t = r: w = r * 20: h = r * 5
    Set lb = Controls.Add("vb.Label", "lb"): With lb: .Move l, t, w, h * 2: l = l + .Width + r: .Caption = s1: .Visible = 1: End With
    Set tx = Controls.Add("vb.TextBox", "tx"): With tx:  .Move l, t, w, h: .Text = 0: .SelStart = 0: .SelLength = 2 ^ 8: .Visible = 1: t = t + .Height + r: End With
    Set cb1 = Controls.Add("vb.CommandButton", "cb1"): With cb1:  .Move l, t, w, h: .Caption = "Далее >>": .Visible = 1: End With
    Set cb2 = Controls.Add("vb.CommandButton", "cb2"): With cb2:  .Move l + w + r, t, w / 2, h: .Caption = "Назад <<": .Visible = 0: End With
    j = Split(s): For i = 0 To UBound(ob)
        h = r * 3: Set ob(i) = Controls.Add("vb.OptionButton", "ob" & i): l = r
        With ob(i)
            .Move l, t, w, h
            .Caption = j(i)
            If i = 0 Then .Value = True
            t = t + h + r
        End With
    Next
    
End Sub

Sub main()
   Dim M As Integer, N As Integer, k As Integer, i As Integer, sum As Long
    M = 5
    N = 122
    k = 3
    For i = M + 1 To N - 1
        If i Mod k = 0 Then sum = sum + i
    Next i
    MsgBox sum
End Sub

Sub main()
   Dim M As Integer, N As Integer, k As Integer, a1 As Integer, an As Integer
    M = 5
    N = 122
    k = 3
    a1 = (M + k) \ k
    an = (N - 1) \ k
    MsgBox k / 2 * (a1 + an) * (an - a1 + 1)
End Sub