Trying to write a VLOOKUP with variables causes RC[1] to not be recognized as a cell refer

Hello,

The code will successfully open files in alphabetical order of name and perform vlookups based on the values in column B. I am having trouble just with one piece of the code. I want to subtract the value in the column to the left from each value. Here is the code I am having a problem with:

Range(Cells(2, pasteColumn), Cells(numD, pasteColumn)).Formula = _
"=VLOOKUP($B2,'[" & strFile & "]" & wshSrc.Name & "'!$B:$AJ,30,FALSE)+VLOOKUP($B2,'[" & strFile & "]" & wshSrc.Name & "'!$B:$AJ,32,FALSE)-IF(ISNUMBER(RC[-1],rc[-1],0)"

It works without the last part:

"=VLOOKUP($B2,'[" & strFile & "]" & wshSrc.Name & "'!$B:$AJ,30,FALSE)+VLOOKUP($B2,'[" & strFile & "]" & wshSrc.Name & "'!$B:$AJ,32,FALSE)"

But I need to subtract the values.

Thanks in advance for help. Here is the full code:

Sub ProcessFiles()
    Dim strPath As String
    Dim strFile As String
    Dim wbkSrc As Workbook
    Dim wshSrc As Worksheet
    Dim wbkTrg As Excel.Workbook
    Dim numD As Long
    Dim pasteColumn As Long
    Set wbkTrg = ActiveWorkbook
    numDealers = Cells(Rows.Count, "A").End(xlUp).Row
    pasteColumn = 3
    With Application.FileDialog(4) ' msoFileDialogFolderPicker
        If .Show Then
            strPath = .SelectedItems(1)
        Else
            MsgBox "You didn't select a folder", vbExclamation
            Exit Sub
        End If
    End With
    Application.ScreenUpdating = False
    If Right(strPath, 1) <> "\" Then
        strPath = strPath & "\"
    End If
    Debug.Print (strPath)
    strFile = Dir(strPath & "*.xls*")
    Do While strFile <> ""
        Set wbkSrc = Workbooks.Open(strPath & strFile)
        Set wshSrc = wbkSrc.Worksheets(1)
        Debug.Print (strFile)
        Debug.Print (wshSrc.Name)
        wbkTrg.Activate
        Debug.Print (pasteColumn)
        Range(Cells(2, pasteColumn), Cells(numD, pasteColumn)).Formula = _
            "=VLOOKUP($B2,'[" & strFile & "]" & wshSrc.Name & "'!$B:$AJ,30,FALSE)+VLOOKUP($B2,'[" & strFile & "]" & wshSrc.Name & "'!$B:$AJ,32,FALSE)-IF(ISNUMBER(RC[-1],rc[-1],0)"
        Range(Cells(2, pasteColumn), Cells(numD, pasteColumn)).Copy
        Range(Cells(2, pasteColumn), Cells(numD, pasteColumn)).PasteSpecial xlPasteValues
        pasteColumn = pasteColumn + 1
        wbkSrc.Close SaveChanges:=False
        strFile = Dir
    Loop
    Application.CutCopyMode = False
    Application.ScreenUpdating = True
End Sub