السلام عليكم
استخدم الكود التالى
Private Sub Worksheet_Change(ByVal Target As Range)
Application.EnableEvents = False
If Target.Column = 2 And ActiveCell.Offset(0, -1).Value = "" Then Exit Sub
Cells(Target.Row, 3).Value = Cells(Target.Row, 1).Value * Cells(Target.Row, 2).Value
Application.EnableEvents = True
End Sub