Option Explicit
Function SumNums(ParamArray nums() As Variant) As Double
    Dim i As Long, j As Long, k As Long
    For i = 0 To UBound(nums)
        If IsArray(nums(i)) Then
            If IsObject(nums(i)) Then
                k = nums(i).Count
            Else
                k = UBound(nums(i))
            End If
            For j = 1 To k
                SumNums = SumNums + Val(nums(i)(j))
            Next j
        Else
            SumNums = SumNums + Val(nums(i))
        End If
    Next i
End Function

=SumNums(D4)-SumNums(D8)