In API of Solidworks, with excel function. Calculate Str.

Private Sub del()

   Dim Str

      Str = "1 + 2"

   Dim Xls As Excel.Application

      Set Xls = GetObject(, "Excel.Application")

      Debug.Print Xls.Evaluate(Str)

      Stop

   Dim SwApp As SldWorks.SldWorks          

End Sub

Help me. How to calculate the string of arithmetic.