VBA FormulaR1C1 syntax with variable - vba

Question

i'm trying to write formula with 2 variables to cell.
formula in cell should be:
=(SUM('C:\Users\[Excel.xlsm]Sheet1'!H:H)-SUM('C:\Users\[Sheet1.xlsm]Sheet1'!I:I))
i want use path to file as variable, as well sheet name.
path = C:\Users\Excel.xlsm 'from msofiledialog
sheetname = Sheet1
what am i missing ?
Cells(1, 1).FormulaR1C1 = "=(SUM('[" & Path & "] " & sheetname & " '!C8) _
-SUM('[" & Path & "] " & sheetname & " '!C9))

Answer 1

thanks, this worked for me :
Sub main
Dim LastRow as String
LastRow = Cells(Rows.Count, 1).End(xlUp).Row
Dim path as String
Path = "C:\users\username\Desktop\"
Dim filename as String
Filename = "Excel.xlsm"
Dim sheetname as String
sheetnameCR = "CR_" & supname
Dim myrangeH as String
Dim myrangeI as String
myrangeH = ("H5:H" & LastRow)
myrangeI = ("I5:I" & LastRow)
Cells(1, 1).Formula = "=SUM('" & Path & "[" & Filename & "]" & sheetnameCR & "'!" & myrangeH & ")" & "-SUM('" & Path & "[" & Filename & "]" & sheetnameCR & "'!" & myrangeI & ")"
End Sub
i had to add "RangeH" variable, because otherwise excel took cell C8, instead of column H, which i wanted.
that's great, but even after i give him full path to desired cell, excel is still asking me for path to excel with FileDialogOpen. any idea why ?