oExcel = CreateObject("Excel.Application")
oExcel.visible = .T.
oExcel.Application.UserControl=.T.
oExcel.Application.Interactive=.T.
oExcel.DisplayAlerts = .F.

oWorkbook = oExcel.Application.Workbooks.Open("&xfile")
oExcel.ActiveSheet.UsedRange.EntireColumn.Autofit
tFormula = "=SUMA(D2:D4)"
tCell = "D5"

oExcel.Range("&tCell").Value = [&tFormula]