Apply formula via macro to unhide row only

Hi,

I'm creating an Excel Template (with vba language) which I going to use at my work place.

Some information in attached excel file
Excel Template.xlsm
ComboBox - was used to hide and unhide row depend on the selection
ActiveX Button 'Name as Update' - was use to calculate the result of cell B6 to B50 (Green Colour Merge cell) with formula

"=SUM(RC[1]:RC[9])/SUM(R[1]C[1]:R[1]C[9])"

Problem facing:
1. How to edit the macro (attach with Update button) to apply formula on the unhide row only
example: Selection "abc on combo Box" - Row 6 to 8 and row 21 to 32 was unhide (Row 9 to 20 and Row 33 to 50 was hide)

2. When row 6 to 11 was unhide, how to teach macro to apply formula on B6, B7, B9 and B10 (but not B8 and B11 as this row as use to visually distinguish between Row 6,7 and Row 9,10).

Thanks in Advance

This smal modification will prevent updating of hidden rows.
See the added IF THEN condition below.

Private Sub CommandButton1_Click()

Dim lastrow As Long

        For rownum = 6 To 50
        If Not Cells(rownum, 2).EntireRow.Hidden Then
          Cells(rownum, 2).Formula = "=SUM(RC[1]:RC[9])/SUM(R[1]C[1]:R[1]C[9])"
        End If
        Next rownum
 

End Sub

you can use another If Then condition to check the interior color of the cells.

Private Sub CommandButton1_Click()
Dim lastrow As Long
        For rownum = 6 To 50
        If Not Cells(rownum, 2).EntireRow.Hidden Then
          asd = Cells(rownum, 2).Interior.ColorIndex
          If Cells(rownum, 2).Interior.ColorIndex = 43 Then
            Cells(rownum, 2).Formula = "=SUM(RC[1]:RC[9])/SUM(R[1]C[1]:R[1]C[9])"
          End If
        End If
        Next rownum
End Sub