Add Funtion to cell

[Oilfield]

Why is this not working?

Private Sub CanPlus()
If InStr(1, ActiveSheet.Range("B2").Value, "CanPlus 750") Then
Range("O10").Formula = (N10 + P10)
End If
End Sub

I want the VBA to drop the funtion "N10 + P10" into Cell O10 if Cell B2 contains the name CanPlus 750